epan/dissectors/packet-mbtcp.c

   1 /* packet-mbtcp.c
   2  * Routines for Modbus/TCP and Modbus/UDP dissection
   3  * By Riaan Swart <rswart@cs.sun.ac.za>
   4  * Copyright 2001, Institute for Applied Computer Science
   5  *                   University of Stellenbosch
   6  *
   7  * See http://www.modbus.org/ for information on Modbus/TCP.
   8  *
   9  * Updated to v1.1b of the Modbus Application Protocol specification
  10  *   Michael Mann * Copyright 2011
  11  *
  12  * Updates Oct/Nov 2012 (Chris Bontje, cbontje[*at*]gmail.com)
  13  * - Some re-factoring to include support for serial Modbus RTU encapsulated in TCP messages
  14  * - Minor text/syntax clean-up
  15  * - Include decoding of holding/input response register data
  16  * - Optionally decode holding/input registers as UINT16, UINT32, 32-bit Float IEEE/Modicon
  17  * - Add various register address formatting options as "Raw", "Modicon 5-digit", "Modicon 6-digit"
  18  *
  19  * Updates Aug 2013 (Chris Bontje)
  20  * - Improved dissection support for serial Modbus RTU with detection of query or response messages
  21  *
  22  *****************************************************************************************************
  23  * A brief explanation of the distinction between Modbus/TCP and Modbus RTU over TCP:
  24  *
  25  * Consider a Modbus poll message: Unit 01, Scan Holding Register Address 0 for 30 Registers
  26  *
  27  * The Modbus/TCP message structure will follow the pattern below:
  28  * 00 00 00 00 00 06 01 03 00 00 00 1E
  29  * AA AA BB BB CC CC DD EE FF FF GG GG
  30  *
  31  * A = 16-bit Transaction Identifier (typically increments, or is locked at zero)
  32  * B = 16-bit Protocol Identifier (typically zero)
  33  * C = 16-bit Length of data payload following (and inclusive of) the length byte
  34  * D = 8-bit Unit / Slave ID
  35  * E = 8-bit Modbus Function Code
  36  * F = 16-bit Reference Number / Register Base Address
  37  * G = 16-bit Word Count / Number of Registers to scan
  38  *
  39  * A identical Modbus RTU (or Modbus RTU over TCP) message will overlay partially with the msg above
  40  * and contain 16-bit CRC at the end:
  41  * 00 00 00 00 00 06 01 03 00 00 00 1E -- -- (Modbus/TCP message, repeated from above)
  42  * -- -- -- -- -- -- 01 03 00 00 00 1E C5 C2 (Modbus RTU over TCP message, includes 16-bit CRC footer)
  43  * AA AA BB BB CC CC DD EE FF FF GG GG HH HH
  44  *
  45  * A = Not present in Modbus RTU message
  46  * B = Not present in Modbus RTU message
  47  * C = Not present in Modbus RTU message
  48  * D = 8-bit Unit / Slave ID
  49  * E = 8-bit Modbus Function Code
  50  * F = 16-bit Reference Number / Register Base Address
  51  * G = 16-bit Word Count / Number of Registers to scan
  52  * H = 16-bit CRC
  53  *
  54  *****************************************************************************************************
  55  * $Id$
  56  *
  57  * Wireshark - Network traffic analyzer
  58  * By Gerald Combs <gerald@wireshark.org>
  59  * Copyright 1998 Gerald Combs
  60  *
  61  * This program is free software; you can redistribute it and/or
  62  * modify it under the terms of the GNU General Public License
  63  * as published by the Free Software Foundation; either version 2
  64  * of the License, or (at your option) any later version.
  65  *
  66  * This program is distributed in the hope that it will be useful,
  67  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  68  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  69  * GNU General Public License for more details.
  70  *
  71  * You should have received a copy of the GNU General Public License
  72  * along with this program; if not, write to the Free Software
  73  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  74  */
  75
  76 #include "config.h"
  77
  78 #include <epan/packet.h>
  79 #include <epan/wmem/wmem.h>
  80 #include "packet-tcp.h"
  81 #include "packet-mbtcp.h"
  82 #include <epan/prefs.h>
  83 #include <epan/expert.h>
  84 #include <epan/crc16-tvb.h> /* For CRC verification */\
  85
  86 /* Initialize the protocol and registered fields */
  87 static int proto_mbtcp = -1;
  88 static int proto_mbrtu = -1;
  89 static int proto_modbus = -1;
  90 static int hf_mbtcp_transid = -1;
  91 static int hf_mbtcp_protid = -1;
  92 static int hf_mbtcp_len = -1;
  93 static int hf_mbtcp_unitid = -1;
  94 static int hf_mbtcp_functioncode = -1;
  95 static int hf_modbus_reference = -1;
  96 static int hf_modbus_lreference = -1;
  97 static int hf_modbus_reftype = -1;
  98 static int hf_modbus_readref = -1;
  99 static int hf_modbus_writeref = -1;
 100 static int hf_modbus_wordcnt = -1;
 101 static int hf_modbus_readwordcnt = -1;
 102 static int hf_modbus_writewordcnt = -1;
 103 static int hf_modbus_bytecnt = -1;
 104 static int hf_modbus_lbytecnt = -1;
 105 static int hf_modbus_bitcnt = -1;
 106 static int hf_modbus_exceptioncode = -1;
 107 static int hf_modbus_diag_sf = -1;
 108 static int hf_modbus_diag_return_query_data_request = -1;
 109 static int hf_modbus_diag_return_query_data_echo = -1;
 110 static int hf_modbus_diag_restart_communication_option = -1;
 111 static int hf_modbus_diag_return_diag_register = -1;
 112 static int hf_modbus_diag_ascii_input_delimiter = -1;
 113 static int hf_modbus_diag_return_bus_message_count = -1;
 114 static int hf_modbus_diag_return_bus_comm_error_count = -1;
 115 static int hf_modbus_diag_return_bus_exception_error_count = -1;
 116 static int hf_modbus_diag_return_slave_message_count = -1;
 117 static int hf_modbus_diag_return_no_slave_response_count = -1;
 118 static int hf_modbus_diag_return_slave_nak_count = -1;
 119 static int hf_modbus_diag_return_slave_busy_count = -1;
 120 static int hf_modbus_diag_return_bus_char_overrun_count = -1;
 121 static int hf_modbus_status = -1;
 122 static int hf_modbus_event_count = -1;
 123 static int hf_modbus_message_count = -1;
 124 static int hf_modbus_event_recv_comm_err = -1;
 125 static int hf_modbus_event_recv_char_over = -1;
 126 static int hf_modbus_event_recv_lo_mode = -1;
 127 static int hf_modbus_event_recv_broadcast = -1;
 128 static int hf_modbus_event_send_read_ex = -1;
 129 static int hf_modbus_event_send_slave_abort_ex = -1;
 130 static int hf_modbus_event_send_slave_busy_ex = -1;
 131 static int hf_modbus_event_send_slave_nak_ex = -1;
 132 static int hf_modbus_event_send_write_timeout = -1;
 133 static int hf_modbus_event_send_lo_mode = -1;
 134 static int hf_modbus_andmask = -1;
 135 static int hf_modbus_ormask = -1;
 136 static int hf_modbus_data = -1;
 137 static int hf_modbus_mei = -1;
 138 static int hf_modbus_read_device_id = -1;
 139 static int hf_modbus_object_id = -1;
 140 static int hf_modbus_num_objects = -1;
 141 static int hf_modbus_list_object_len = -1;
 142 static int hf_modbus_conformity_level = -1;
 143 static int hf_modbus_more_follows = -1;
 144 static int hf_modbus_next_object_id = -1;
 145 static int hf_modbus_object_str_value = -1;
 146 static int hf_modbus_reg_uint16 = -1;
 147 static int hf_modbus_reg_uint32 = -1;
 148 static int hf_modbus_reg_ieee_float = -1;
 149 static int hf_modbus_reg_modicon_float = -1;
 150 static int hf_mbrtu_unitid = -1;
 151 static int hf_mbrtu_crc16 = -1;
 152
 153 /* Initialize the subtree pointers */
 154 static gint ett_mbtcp = -1;
 155 static gint ett_mbrtu = -1;
 156 static gint ett_modbus_hdr = -1;
 157 static gint ett_group_hdr = -1;
 158 static gint ett_events = -1;
 159 static gint ett_events_recv = -1;
 160 static gint ett_events_send = -1;
 161 static gint ett_device_id_objects = -1;
 162 static gint ett_device_id_object_items = -1;
 163
 164 static expert_field ei_mbrtu_crc16_incorrect = EI_INIT;
 165 static expert_field ei_modbus_data_decode = EI_INIT;
 166
 167 static dissector_handle_t modbus_handle;
 168 static dissector_handle_t mbtcp_handle;
 169 static dissector_handle_t mbrtu_handle;
 170
 171 static dissector_table_t   modbus_data_dissector_table;
 172 static dissector_table_t   modbus_dissector_table;
 173
 174
 175 /* Globals for Modbus/TCP Preferences */
 176 static gboolean mbtcp_desegment = TRUE;
 177 static guint global_mbus_tcp_port = PORT_MBTCP; /* Port 502, by default */
 178 static gint global_mbus_tcp_register_format = MBTCP_PREF_REGISTER_FORMAT_UINT16;
 179 static gint global_mbus_tcp_register_addr_type = MBTCP_PREF_REGISTER_ADDR_RAW;
 180
 181 /* Globals for Modbus RTU over TCP Preferences */
 182 static gboolean mbrtu_desegment = TRUE;
 183 static guint global_mbus_rtu_port = PORT_MBRTU; /* 0, by default        */
 184 static gint global_mbus_rtu_register_format = MBTCP_PREF_REGISTER_FORMAT_UINT16;
 185 static gint global_mbus_rtu_register_addr_type = MBTCP_PREF_REGISTER_ADDR_RAW;
 186 static gboolean mbrtu_crc = FALSE;
 187
 188 static int
 189 classify_mbtcp_packet(packet_info *pinfo)
 190 {
 191     /* see if nature of packets can be derived from src/dst ports */
 192     /* if so, return as found */
 193     /*                        */
 194     /* XXX Update Oct 2012 - It can be difficult to determine if a packet is a query or response; some way to track  */
 195     /* the Modbus/TCP transaction ID for each pair of messages would allow for detection based on a new seq. number. */
 196     /* Otherwise, we can stick with this method; a configurable port option has been added to allow for usage of     */
 197     /* user ports either than the default of 502.                                                                    */
 198     if (( pinfo->srcport == global_mbus_tcp_port ) && ( pinfo->destport != global_mbus_tcp_port ))
 199         return RESPONSE_PACKET;
 200     if (( pinfo->srcport != global_mbus_tcp_port ) && ( pinfo->destport == global_mbus_tcp_port ))
 201         return QUERY_PACKET;
 202
 203     /* else, cannot classify */
 204     return CANNOT_CLASSIFY;
 205 }
 206
 207 static int
 208 classify_mbrtu_packet(packet_info *pinfo, tvbuff_t *tvb)
 209 {
 210     /* see if nature of packets can be derived from src/dst ports */
 211     /* if so, return as found */
 212     if (( pinfo->srcport == global_mbus_rtu_port ) && ( pinfo->destport != global_mbus_rtu_port ))
 213         return RESPONSE_PACKET;
 214     if (( pinfo->srcport != global_mbus_rtu_port ) && ( pinfo->destport == global_mbus_rtu_port ))
 215         return QUERY_PACKET;
 216
 217     /* Special case for serial-captured packets that don't have an Ethernet header */
 218     /* Dig into these a little deeper to try to guess the message type */
 219     if (!pinfo->srcport) {
 220         /* If length is 8, this is either a query or very short response */
 221         if (tvb_length(tvb) == 8) {
 222             /* Only possible to get a response message of 8 bytes with Discrete or Coils */
 223             if ((tvb_get_guint8(tvb, 1) == READ_COILS) || (tvb_get_guint8(tvb, 1) == READ_DISCRETE_INPUTS)) {
 224                 /* If this is, in fact, a response then the data byte count will be 3 */
 225                 /* This will correctly identify all messages except for those that are discrete or coil polls */
 226                 /* where the base address range happens to have 0x03 in the upper 16-bit address register     */
 227                 if (tvb_get_guint8(tvb, 2) == 3) {
 228                     return RESPONSE_PACKET;
 229                 }
 230                 else {
 231                     return QUERY_PACKET;
 232                 }
 233             }
 234             else {
 235                 return QUERY_PACKET;
 236             }
 237         }
 238         else {
 239             return RESPONSE_PACKET;
 240         }
 241     }
 242
 243     /* else, cannot classify */
 244     return CANNOT_CLASSIFY;
 245 }
 246
 247 /* Translate function to string, as given on p6 of
 248  * "Open Modbus/TCP Specification", release 1 by Andy Swales.
 249  */
 250 static const value_string function_code_vals[] = {
 251     { READ_COILS,             "Read Coils" },
 252     { READ_DISCRETE_INPUTS,   "Read Discrete Inputs" },
 253     { READ_HOLDING_REGS,      "Read Holding Registers" },
 254     { READ_INPUT_REGS,        "Read Input Registers" },
 255     { WRITE_SINGLE_COIL,      "Write Single Coil" },
 256     { WRITE_SINGLE_REG,       "Write Single Register" },
 257     { READ_EXCEPT_STAT,       "Read Exception Status" },
 258     { DIAGNOSTICS,            "Diagnostics" },
 259     { GET_COMM_EVENT_CTRS,    "Get Comm. Event Counters" },
 260     { GET_COMM_EVENT_LOG,     "Get Comm. Event Log" },
 261     { WRITE_MULT_COILS,       "Write Multiple Coils" },
 262     { WRITE_MULT_REGS,        "Write Multiple Registers" },
 263     { REPORT_SLAVE_ID,        "Report Slave ID" },
 264     { READ_FILE_RECORD,       "Read File Record" },
 265     { WRITE_FILE_RECORD,      "Write File Record" },
 266     { MASK_WRITE_REG,         "Mask Write Register" },
 267     { READ_WRITE_REG,         "Read Write Register" },
 268     { READ_FIFO_QUEUE,        "Read FIFO Queue" },
 269     { ENCAP_INTERFACE_TRANSP, "Encapsulated Interface Transport" },
 270     { 0,                      NULL }
 271 };
 272
 273 /* Translate exception code to string */
 274 static const value_string exception_code_vals[] = {
 275     { ILLEGAL_FUNCTION,    "Illegal function" },
 276     { ILLEGAL_ADDRESS,     "Illegal data address" },
 277     { ILLEGAL_VALUE,       "Illegal data value" },
 278     { SLAVE_FAILURE,       "Slave device failure" },
 279     { ACKNOWLEDGE,         "Acknowledge" },
 280     { SLAVE_BUSY,          "Slave device busy" },
 281     { MEMORY_ERR,          "Memory parity error" },
 282     { GATEWAY_UNAVAILABLE, "Gateway path unavailable" },
 283     { GATEWAY_TRGT_FAIL,   "Gateway target device failed to respond" },
 284     { 0,                    NULL }
 285 };
 286
 287 /* Translate Modbus Encapsulation Interface (MEI) code to string */
 288 static const value_string encap_interface_code_vals[] = {
 289     { CANOPEN_REQ_RESP, "CANopen Request/Response " },
 290     { READ_DEVICE_ID,   "Read Device Identification" },
 291     { 0,                NULL }
 292 };
 293
 294 /* Translate Modbus Diagnostic subfunction code to string */
 295 static const value_string diagnostic_code_vals[] = {
 296     { RETURN_QUERY_DATA,                "Return Query Data" },
 297     { RESTART_COMMUNICATION_OPTION,     "Restart Communications Option" },
 298     { RETURN_DIAGNOSTIC_REGISTER,       "Return Diagnostic Register" },
 299     { CHANGE_ASCII_INPUT_DELIMITER,     "Change ASCII Input Delimiter" },
 300     { FORCE_LISTEN_ONLY_MODE,           "Force Listen Only Mode" },
 301     { CLEAR_COUNTERS_AND_DIAG_REG,      "Clear Counters and Diagnostic Register" },
 302     { RETURN_BUS_MESSAGE_COUNT,         "Return Bus Message Count" },
 303     { RETURN_BUS_COMM_ERROR_COUNT,      "Return Bus Communication Error Count" },
 304     { RETURN_BUS_EXCEPTION_ERROR_COUNT, "Return Bus Exception Error Count" },
 305     { RETURN_SLAVE_MESSAGE_COUNT,       "Return Slave Message Count" },
 306     { RETURN_SLAVE_NO_RESPONSE_COUNT,   "Return Slave No Response Count" },
 307     { RETURN_SLAVE_NAK_COUNT,           "Return Slave NAK Count" },
 308     { RETURN_SLAVE_BUSY_COUNT,          "Return Slave Busy Count" },
 309     { RETURN_BUS_CHAR_OVERRUN_COUNT,    "Return Bus Character Overrun Count" },
 310     { CLEAR_OVERRUN_COUNTER_AND_FLAG,   "Clear Overrun Counter and Flag" },
 311     { 0,                                NULL }
 312 };
 313
 314 static const value_string diagnostic_restart_communication_option_vals[] = {
 315     { 0,        "Leave Log" },
 316     { 0xFF,     "Clear Log" },
 317     { 0,        NULL }
 318 };
 319
 320 /* Translate read device code to string */
 321 static const value_string read_device_id_vals[] = {
 322     { 1,        "Basic Device Identification" },
 323     { 2,        "Regular Device Identification"  },
 324     { 3,        "Extended Device Identification"  },
 325     { 4,        "Specific Identification Object"  },
 326
 327     { 0,        NULL             }
 328 };
 329
 330 /* Translate read device code to string */
 331 static const value_string object_id_vals[] = {
 332     { 0,        "VendorName" },
 333     { 1,        "ProductCode" },
 334     { 2,        "MajorMinorRevision"  },
 335     { 3,        "VendorURL"  },
 336     { 4,        "ProductName"  },
 337     { 5,        "ModelName"  },
 338     { 6,        "UserApplicationName"  },
 339
 340     { 0,        NULL             }
 341 };
 342
 343 static const value_string conformity_level_vals[] = {
 344     { 0x01,     "Basic Device Identification (stream)" },
 345     { 0x02,     "Regular Device Identification (stream)"  },
 346     { 0x03,     "Extended Device Identification (stream)"  },
 347     { 0x81,     "Basic Device Identification (stream and individual)" },
 348     { 0x82,     "Regular Device Identification (stream and individual)"  },
 349     { 0x83,     "Extended Device Identification (stream and individual)"  },
 350
 351     { 0,        NULL             }
 352 };
 353
 354 static const enum_val_t mbus_register_format[] = {
 355   { "UINT16     ", "UINT16     ",  MBTCP_PREF_REGISTER_FORMAT_UINT16  },
 356   { "UINT32     ", "UINT32     ",  MBTCP_PREF_REGISTER_FORMAT_UINT32  },
 357   { "IEEE FLT   ", "IEEE FLT   ",  MBTCP_PREF_REGISTER_FORMAT_IEEE_FLOAT  },
 358   { "MODICON FLT", "MODICON FLT",  MBTCP_PREF_REGISTER_FORMAT_MODICON_FLOAT  },
 359   { NULL, NULL, 0 }
 360 };
 361
 362 static const enum_val_t mbus_register_addr_type[] = {
 363   { "RAW            ", "RAW            ",  MBTCP_PREF_REGISTER_ADDR_RAW  },
 364   { "MODICON 5-DIGIT", "MODICON 5-DIGIT",  MBTCP_PREF_REGISTER_ADDR_MOD5  },
 365   { "MODICON 6-DIGIT", "MODICON 6-DIGIT",  MBTCP_PREF_REGISTER_ADDR_MOD6  },
 366   { NULL, NULL, 0 }
 367 };
 368
 369 /* Code to dissect Modbus/TCP packets */
 370 static int
 371 dissect_mbtcp_pdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
 372 {
 373 /* Set up structures needed to add the protocol subtree and manage it */
 374     proto_item    *mi;
 375     proto_tree    *mbtcp_tree;
 376     int           offset, packet_type;
 377     tvbuff_t      *next_tvb;
 378     const char    *func_string = "";
 379     const char    *pkt_type_str = "";
 380     const char    *err_str = "";
 381     guint16       transaction_id, protocol_id, len;
 382     guint8        unit_id, function_code, exception_code, subfunction_code;
 383     void          *p_save_proto_data;
 384     modbus_request_info_t *request_info;
 385
 386     /* Make entries in Protocol column on summary display */
 387     col_set_str(pinfo->cinfo, COL_PROTOCOL, "Modbus/TCP");
 388     col_clear(pinfo->cinfo, COL_INFO);
 389
 390     transaction_id = tvb_get_ntohs(tvb, 0);
 391     protocol_id = tvb_get_ntohs(tvb, 2);
 392     len = tvb_get_ntohs(tvb, 4);
 393
 394     unit_id = tvb_get_guint8(tvb, 6);
 395     function_code = tvb_get_guint8(tvb, 7) & 0x7F;
 396
 397     /* Make entries in Info column on summary display */
 398     offset = 0;
 399
 400     /* Find exception - last bit set in function code */
 401     if (tvb_get_guint8(tvb, 7) & 0x80) {
 402         exception_code = tvb_get_guint8(tvb, offset + 8);
 403     }
 404     else {
 405         exception_code = 0;
 406     }
 407
 408     if ((function_code == ENCAP_INTERFACE_TRANSP) && (exception_code == 0))  {
 409         func_string = val_to_str_const(tvb_get_guint8(tvb, offset + 8), encap_interface_code_vals, "Encapsulated Interface Transport");
 410         subfunction_code = 1;
 411     }
 412     else if ((function_code == DIAGNOSTICS) && (exception_code == 0))  {
 413         func_string = val_to_str_const(tvb_get_ntohs(tvb, offset + 8), diagnostic_code_vals, "Diagnostics");
 414         subfunction_code = 1;
 415     }
 416     else {
 417         func_string = val_to_str(function_code, function_code_vals, "Unknown function (%d)");
 418         subfunction_code = 0;
 419     }
 420
 421     /* "Request" or "Response" */
 422     packet_type = classify_mbtcp_packet(pinfo);
 423
 424     switch ( packet_type ) {
 425         case QUERY_PACKET :
 426             pkt_type_str="Query";
 427             break;
 428         case RESPONSE_PACKET :
 429             pkt_type_str="Response";
 430             break;
 431         case CANNOT_CLASSIFY :
 432             err_str="Unable to classify as query or response.";
 433             pkt_type_str="unknown";
 434             break;
 435         default :
 436             break;
 437     }
 438     if ( exception_code != 0 )
 439         err_str="Exception returned ";
 440
 441     if (subfunction_code == 0) {
 442         if (strlen(err_str) > 0) {
 443             col_add_fstr(pinfo->cinfo, COL_INFO,
 444                     "%8s: Trans: %5u; Unit: %3u, Func: %3u: %s. %s",
 445                     pkt_type_str, transaction_id, unit_id,
 446                     function_code, func_string, err_str);
 447         }
 448         else {
 449             col_add_fstr(pinfo->cinfo, COL_INFO,
 450                     "%8s: Trans: %5u; Unit: %3u, Func: %3u: %s",
 451                     pkt_type_str, transaction_id, unit_id,
 452                     function_code, func_string);
 453         }
 454     }
 455     else {
 456         if (strlen(err_str) > 0) {
 457             col_add_fstr(pinfo->cinfo, COL_INFO,
 458                     "%8s: Trans: %5u; Unit: %3u, Func: %3u/%3u: %s. %s",
 459                     pkt_type_str, transaction_id, unit_id,
 460                     function_code, subfunction_code, func_string, err_str);
 461         }
 462         else {
 463             col_add_fstr(pinfo->cinfo, COL_INFO,
 464                     "%8s: Trans: %5u; Unit: %3u, Func: %3u/%3u: %s",
 465                     pkt_type_str, transaction_id, unit_id,
 466                     function_code, subfunction_code, func_string);
 467         }
 468     }
 469
 470     mi = proto_tree_add_protocol_format(tree, proto_mbtcp, tvb, offset,
 471             len+6, "Modbus/TCP");
 472     mbtcp_tree = proto_item_add_subtree(mi, ett_mbtcp);
 473
 474     /* Add items to protocol tree specific to Modbus/TCP */
 475     proto_tree_add_uint(mbtcp_tree, hf_mbtcp_transid, tvb, offset, 2, transaction_id);
 476     proto_tree_add_uint(mbtcp_tree, hf_mbtcp_protid, tvb, offset + 2, 2, protocol_id);
 477     proto_tree_add_uint(mbtcp_tree, hf_mbtcp_len, tvb, offset + 4, 2, len);
 478     proto_tree_add_uint(mbtcp_tree, hf_mbtcp_unitid, tvb, offset + 6, 1, unit_id);
 479
 480     /* dissect the Modbus PDU */
 481     next_tvb = tvb_new_subset( tvb, offset+7, len-1, len-1);
 482
 483     /* keep existing context */
 484     p_save_proto_data = p_get_proto_data( pinfo->fd, proto_modbus, 0 );
 485     p_remove_proto_data(pinfo->fd, proto_modbus, 0);
 486
 487     /* Create enough context for Modbus dissector */
 488     request_info = wmem_new(wmem_packet_scope(), modbus_request_info_t);
 489     request_info->packet_type = (guint8)packet_type;
 490     request_info->register_addr_type = (guint8)global_mbus_tcp_register_addr_type;
 491     request_info->register_format = (guint8)global_mbus_tcp_register_format;
 492     p_add_proto_data(pinfo->fd, proto_modbus, 0, request_info);
 493
 494     /* Continue with dissection of Modbus data payload following Modbus/TCP frame */
 495     if( tvb_length_remaining(tvb, offset) > 0 )
 496         call_dissector(modbus_handle, next_tvb, pinfo, tree);
 497
 498     p_remove_proto_data(pinfo->fd, proto_modbus, 0);
 499     p_add_proto_data(pinfo->fd, proto_modbus, 0, p_save_proto_data);
 500     return tvb_length(tvb);
 501 }
 502
 503 /* Code to dissect Modbus RTU over TCP packets */
 504 static int
 505 dissect_mbrtu_pdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
 506 {
 507 /* Set up structures needed to add the protocol subtree and manage it */
 508     proto_item    *mi, *crc_item;
 509     proto_tree    *mbrtu_tree;
 510     gint           offset, packet_type;
 511     tvbuff_t      *next_tvb;
 512     const char    *func_string = "";
 513     const char    *pkt_type_str = "";
 514     const char    *err_str = "";
 515     guint16       len, crc16, calc_crc16;
 516     guint8        unit_id, function_code, exception_code, subfunction_code;
 517     void          *p_save_proto_data;
 518     modbus_request_info_t *request_info;
 519
 520     /* Make entries in Protocol column on summary display */
 521     col_set_str(pinfo->cinfo, COL_PROTOCOL, "Modbus RTU");
 522     col_clear(pinfo->cinfo, COL_INFO);
 523
 524     len = tvb_length(tvb);
 525
 526     unit_id = tvb_get_guint8(tvb, 0);
 527     function_code = tvb_get_guint8(tvb, 1) & 0x7F;
 528     crc16 = tvb_get_ntohs(tvb, len-2);
 529
 530     /* Make entries in Info column on summary display */
 531     offset = 0;
 532
 533     /* Find exception - last bit set in function code */
 534     if (tvb_get_guint8(tvb, 1) & 0x80) {
 535         exception_code = tvb_get_guint8(tvb, offset + 2);
 536     }
 537     else {
 538         exception_code = 0;
 539     }
 540
 541     if ((function_code == ENCAP_INTERFACE_TRANSP) && (exception_code == 0))  {
 542         func_string = val_to_str_const(tvb_get_guint8(tvb, offset + 2), encap_interface_code_vals, "Encapsulated Interface Transport");
 543         subfunction_code = 1;
 544     }
 545     else if ((function_code == DIAGNOSTICS) && (exception_code == 0))  {
 546         func_string = val_to_str_const(tvb_get_ntohs(tvb, offset + 2), diagnostic_code_vals, "Diagnostics");
 547         subfunction_code = 1;
 548     }
 549     else {
 550         func_string = val_to_str(function_code, function_code_vals, "Unknown function (%d)");
 551         subfunction_code = 0;
 552     }
 553
 554     /* "Request" or "Response" */
 555     packet_type = classify_mbrtu_packet(pinfo, tvb);
 556
 557     switch ( packet_type ) {
 558         case QUERY_PACKET :
 559             pkt_type_str="Query";
 560             break;
 561         case RESPONSE_PACKET :
 562             pkt_type_str="Response";
 563             break;
 564         case CANNOT_CLASSIFY :
 565             err_str="Unable to classify as query or response.";
 566             pkt_type_str="unknown";
 567             break;
 568         default :
 569             break;
 570     }
 571     if ( exception_code != 0 )
 572         err_str="Exception returned ";
 573
 574     if (subfunction_code == 0) {
 575         if (strlen(err_str) > 0) {
 576             col_add_fstr(pinfo->cinfo, COL_INFO,
 577                     "%8s: Unit: %3u, Func: %3u: %s. %s",
 578                     pkt_type_str, unit_id,
 579                     function_code, func_string, err_str);
 580         }
 581         else {
 582             col_add_fstr(pinfo->cinfo, COL_INFO,
 583                     "%8s: Unit: %3u, Func: %3u: %s",
 584                     pkt_type_str, unit_id,
 585                     function_code, func_string);
 586         }
 587     }
 588     else {
 589         if (strlen(err_str) > 0) {
 590             col_add_fstr(pinfo->cinfo, COL_INFO,
 591                     "%8s: Unit: %3u, Func: %3u/%3u: %s. %s",
 592                     pkt_type_str, unit_id,
 593                     function_code, subfunction_code, func_string, err_str);
 594         }
 595         else {
 596             col_add_fstr(pinfo->cinfo, COL_INFO,
 597                     "%8s: Unit: %3u, Func: %3u/%3u: %s",
 598                     pkt_type_str, unit_id,
 599                     function_code, subfunction_code, func_string);
 600         }
 601     }
 602
 603     mi = proto_tree_add_protocol_format(tree, proto_mbrtu, tvb, offset,
 604             len, "Modbus RTU");
 605     mbrtu_tree = proto_item_add_subtree(mi, ett_mbrtu);
 606
 607     /* Add items to protocol tree specific to Modbus RTU */
 608     proto_tree_add_uint(mbrtu_tree, hf_mbrtu_unitid, tvb, offset, 1, unit_id);
 609     crc_item = proto_tree_add_uint(mbrtu_tree, hf_mbrtu_crc16, tvb, len-2, 2, crc16);
 610
 611     /* CRC validation */
 612     if (mbrtu_crc)
 613     {
 614         calc_crc16 = crc16_plain_tvb_offset_seed(tvb, offset, len-2, 0xFFFF);
 615         if (g_htons(calc_crc16) != crc16)
 616             expert_add_info_format(pinfo, crc_item, &ei_mbrtu_crc16_incorrect, "Incorrect CRC - should be 0x%04x", g_htons(calc_crc16));
 617     }
 618
 619     /* make sure to ignore the CRC-16 footer bytes */
 620     len = len - 2;
 621
 622     /* dissect the Modbus PDU                      */
 623     next_tvb = tvb_new_subset( tvb, offset+1, len-1, len-1);
 624
 625     /* keep existing context */
 626     p_save_proto_data = p_get_proto_data( pinfo->fd, proto_modbus, 0 );
 627     p_remove_proto_data(pinfo->fd, proto_modbus, 0);
 628
 629     /* Create enough context for Modbus dissector */
 630     request_info = wmem_new(wmem_packet_scope(), modbus_request_info_t);
 631     request_info->packet_type = (guint8)packet_type;
 632     request_info->register_addr_type = (guint8)global_mbus_rtu_register_addr_type;
 633     request_info->register_format = (guint8)global_mbus_rtu_register_format;
 634     p_add_proto_data(pinfo->fd, proto_modbus, 0, request_info);
 635
 636     /* Continue with dissection of Modbus data payload following Modbus RTU frame */
 637     if( tvb_length_remaining(tvb, offset) > 0 )
 638         call_dissector(modbus_handle, next_tvb, pinfo, tree);
 639
 640     p_remove_proto_data(pinfo->fd, proto_modbus, 0);
 641     p_add_proto_data(pinfo->fd, proto_modbus, 0, p_save_proto_data);
 642     return tvb_length(tvb);
 643 }
 644
 645
 646 /* Return length of Modbus/TCP message */
 647 static guint
 648 get_mbtcp_pdu_len(packet_info *pinfo _U_, tvbuff_t *tvb, int offset)
 649 {
 650     guint16 plen;
 651
 652     /*
 653      * Get the length of the data from the encapsulation header.
 654      */
 655     plen = tvb_get_ntohs(tvb, offset + 4);
 656
 657     /*
 658      * That length doesn't include the encapsulation header itself;
 659      * add that in.
 660      */
 661     return plen + 6;
 662 }
 663
 664 /* Return length of Modbus RTU over TCP message */
 665 static guint
 666 get_mbrtu_pdu_len(packet_info *pinfo _U_, tvbuff_t *tvb, int offset _U_)
 667 {
 668
 669     /* Modbus/TCP frames include a "length" word in each message; Modbus RTU over TCP does not, so don't attempt to get one */
 670     return tvb_length(tvb);
 671 }
 672
 673
 674 /* Code to dissect Modbus/TCP messages */
 675 static int
 676 dissect_mbtcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data)
 677 {
 678
 679     /* Make sure there's at least enough data to determine it's a Modbus TCP packet */
 680     if (!tvb_bytes_exist(tvb, 0, 8))
 681         return 0;
 682
 683     /* check that it actually looks like Modbus/TCP */
 684     /* protocol id == 0 */
 685     if(tvb_get_ntohs(tvb, 2) != 0 ){
 686         return 0;
 687     }
 688     /* length is at least 2 (unit_id + function_code) */
 689     if(tvb_get_ntohs(tvb, 4) < 2 ){
 690         return 0;
 691     }
 692
 693     /* build up protocol tree and iterate over multiple packets */
 694     tcp_dissect_pdus(tvb, pinfo, tree, mbtcp_desegment, 6,
 695                      get_mbtcp_pdu_len, dissect_mbtcp_pdu, data);
 696
 697     return tvb_length(tvb);
 698 }
 699
 700 /* Code to dissect Modbus RTU over TCP messages */
 701 static int
 702 dissect_mbrtu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data)
 703 {
 704
 705     /* Make sure there's at least enough data to determine it's a Modbus packet */
 706     if (!tvb_bytes_exist(tvb, 0, 6))
 707         return 0;
 708
 709     /* For Modbus RTU mode, confirm that the first byte is a valid address (non-zero), */
 710     /* so we can eliminate false-posititves on Modbus TCP messages loaded as RTU       */
 711     if(tvb_get_guint8(tvb, 0) == 0 )
 712         return 0;
 713
 714     /* build up protocol tree and iterate over multiple packets */
 715     tcp_dissect_pdus(tvb, pinfo, tree, mbrtu_desegment, 6,
 716                      get_mbrtu_pdu_len, dissect_mbrtu_pdu, data);
 717
 718     return tvb_length(tvb);
 719 }
 720
 721
 722 /* Code to allow further dissection of Modbus data payload */
 723 /* Common to both Modbus/TCP and Modbus RTU dissectors     */
 724 static void
 725 dissect_modbus_data(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint8 function_code,
 726                     gint payload_start, gint payload_len, guint8 register_format)
 727 {
 728     gint reported_len, data_offset, reg_num = 0;
 729     guint16 data16, modflt_lo, modflt_hi;
 730     guint32 data32, modflt_comb;
 731     gfloat data_float, modfloat;
 732     proto_item    *register_item = NULL;
 733     tvbuff_t *next_tvb;
 734
 735     reported_len = tvb_reported_length_remaining(tvb, payload_start);
 736     data_offset = 0;
 737
 738     if ( payload_start < 0 || ( payload_len + payload_start ) == 0 )
 739         return;
 740
 741     /* If calculated length from remaining tvb data != bytes in packet, do not attempt to decode      */
 742     if ( payload_len != reported_len ) {
 743         proto_tree_add_item(tree, hf_modbus_data, tvb, payload_start, reported_len, ENC_NA);
 744         return;
 745     }
 746
 747     /* If data type of payload is Holding or Input registers */
 748     /* AND */
 749     /* if payload length is not a multiple of 4, don't attempt to decode anything in 32-bit format */
 750     if ((function_code == READ_HOLDING_REGS) || (function_code == READ_INPUT_REGS) || (function_code == WRITE_MULT_REGS)) {
 751         if ((payload_len % 4 != 0) && ( (register_format == MBTCP_PREF_REGISTER_FORMAT_UINT32) ||
 752             (register_format == MBTCP_PREF_REGISTER_FORMAT_IEEE_FLOAT) ||
 753             (register_format == MBTCP_PREF_REGISTER_FORMAT_MODICON_FLOAT) ) ) {
 754             register_item = proto_tree_add_item(tree, hf_modbus_data, tvb, payload_start, payload_len, ENC_NA);
 755             expert_add_info(pinfo, register_item, &ei_modbus_data_decode);
 756             return;
 757         }
 758     }
 759
 760     /* Build a new tvb containing just the data payload   */
 761     next_tvb = tvb_new_subset(tvb, payload_start, payload_len, reported_len);
 762
 763     switch ( function_code ) {
 764
 765         case READ_HOLDING_REGS:
 766         case READ_INPUT_REGS:
 767         case WRITE_MULT_REGS:
 768             while (data_offset < payload_len) {
 769                 /* Use "Preferences" options to determine decoding format of register data, as no format is implied by the protocol itself. */
 770                 /* Based on a standard register size of 16-bits, use decoding format preference to step through each register and display  */
 771                 /* it in an appropriate fashion. */
 772                 switch (register_format) {
 773                     case MBTCP_PREF_REGISTER_FORMAT_UINT16: /* Standard-size unsigned integer 16-bit register */
 774                         data16 = tvb_get_ntohs(next_tvb, data_offset);
 775                         register_item = proto_tree_add_uint(tree, hf_modbus_reg_uint16, next_tvb, data_offset, 2, data16);
 776                         proto_item_set_text(register_item, "Register %u (UINT16): %u", reg_num, data16);
 777
 778                         data_offset += 2;
 779                         reg_num += 1;
 780                         break;
 781                     case MBTCP_PREF_REGISTER_FORMAT_UINT32: /* Double-size unsigned integer 2 x 16-bit registers */
 782                         data32 = tvb_get_ntohl(next_tvb, data_offset);
 783                         register_item = proto_tree_add_uint(tree, hf_modbus_reg_uint32, next_tvb, data_offset, 4, data32);
 784                         proto_item_set_text(register_item, "Register %u (UINT32): %u", reg_num, data32);
 785
 786                         data_offset += 4;
 787                         reg_num += 2;
 788                         break;
 789                     case MBTCP_PREF_REGISTER_FORMAT_IEEE_FLOAT: /* IEEE Floating Point, 2 x 16-bit registers */
 790                         data_float = tvb_get_ntohieee_float(next_tvb, data_offset);
 791                         register_item = proto_tree_add_float(tree, hf_modbus_reg_ieee_float, next_tvb, data_offset, 4, data_float);
 792                         proto_item_set_text(register_item, "Register %u (IEEE Float): %f", reg_num, data_float);
 793
 794                         data_offset += 4;
 795                         reg_num += 2;
 796                         break;
 797                     case MBTCP_PREF_REGISTER_FORMAT_MODICON_FLOAT: /* Modicon Floating Point (word-swap), 2 x 16-bit registers */
 798                         /* Modicon-style Floating Point values are stored in reverse-word order.                     */
 799                         /* ie: a standard IEEE float value 59.991459 is equal to 0x426ff741                          */
 800                         /*     while the Modicon equivalent to this value is 0xf741426f                              */
 801                         /* To re-assemble a proper IEEE float, we must retrieve the 2 x 16-bit words, bit-shift the  */
 802                         /* "hi" component by 16-bits and then OR them together into a combined 32-bit int.           */
 803                         /* Following that operation, use some memcpy magic to copy the 4 raw data bytes from the     */
 804                         /* 32-bit integer into a standard float.  Not sure if there is a cleaner way possible using  */
 805                         /* the Wireshark libaries, but this seems to work OK.                                        */
 806
 807                         modflt_lo = tvb_get_ntohs(next_tvb, data_offset);
 808                         modflt_hi = tvb_get_ntohs(next_tvb, data_offset+2);
 809                         modflt_comb = (guint32)(modflt_hi<<16) | modflt_lo;
 810                         memcpy(&modfloat, &modflt_comb, 4);
 811
 812                         register_item = proto_tree_add_float(tree, hf_modbus_reg_modicon_float, next_tvb, data_offset, 4, modfloat);
 813                         proto_item_set_text(register_item, "Register %u (Modicon Float): %f", reg_num, modfloat);
 814
 815                         data_offset += 4;
 816                         reg_num += 2;
 817                         break;
 818                     default:
 819                         /* Avoid any chance of an infinite loop */
 820                         data_offset = payload_len;
 821                         break;
 822                     } /* register format switch */
 823
 824                 } /* while loop */
 825
 826                 break;
 827
 828         default:
 829             if ( ! dissector_try_string(modbus_data_dissector_table, "data", next_tvb, pinfo, tree, NULL) )
 830                 proto_tree_add_item(tree, hf_modbus_data, tvb, payload_start, payload_len, ENC_NA);
 831             break;
 832         }
 833 }
 834
 835 /* Code to actually dissect the packets */
 836 static int
 837 dissect_modbus(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_)
 838 {
 839     proto_tree    *modbus_tree, *group_tree, *event_tree,
 840                   *event_item_tree, *device_objects_tree,
 841                   *device_objects_item_tree;
 842     proto_item    *mi, *mf, *me, *mei, *doe, *doie;
 843     int           offset = 0, group_offset;
 844     gint          payload_start, payload_len, event_index,
 845                   ii, byte_cnt, len, num_objects, object_index,
 846                   object_len;
 847     guint32       group_byte_cnt, group_word_cnt;
 848     guint8        function_code, exception_code, mei_code, event_code, object_type;
 849     guint8        packet_type, register_format; /*register_addr_type*/
 850     guint16       diagnostic_code;
 851     modbus_request_info_t *request_info;
 852
 853     /* Don't need to do anything if there's no tree */
 854     if (tree == NULL)
 855         return tvb_length(tvb);
 856
 857     len = tvb_length_remaining(tvb, 0);
 858
 859     /* If the packet is zero-length, we should not attempt to dissect any further */
 860     if (len == 0)
 861         return 0;
 862
 863     function_code = tvb_get_guint8(tvb, offset) & 0x7F;
 864
 865     /* Find exception - last bit set in function code */
 866     if (tvb_get_guint8(tvb, offset) & 0x80 ) {
 867         exception_code = tvb_get_guint8(tvb, offset+1);
 868     }
 869     else {
 870         exception_code = 0;
 871     }
 872
 873     /* See if we have any context */
 874     request_info = (modbus_request_info_t *)p_get_proto_data( pinfo->fd, proto_modbus, 0 );
 875     if (request_info != NULL)
 876     {
 877         packet_type = request_info->packet_type;
 878         register_format = request_info->register_format;
 879         /*register_addr_type = request_info->register_addr_type;*/
 880     }
 881     else
 882     {
 883         /* Default to a response packet to at least attempt to decode a good chunk of data */
 884         packet_type = RESPONSE_PACKET;
 885         register_format = MBTCP_PREF_REGISTER_FORMAT_UINT16;
 886        /* register_addr_type = MBTCP_PREF_REGISTER_ADDR_RAW;*/
 887     }
 888
 889     /* Add items to protocol tree specific to Modbus generic */
 890     mf = proto_tree_add_text(tree, tvb, offset, len, "Modbus");
 891     modbus_tree = proto_item_add_subtree(mf, ett_modbus_hdr);
 892
 893     mi = proto_tree_add_uint(modbus_tree, hf_mbtcp_functioncode, tvb, offset, 1,
 894                              function_code);
 895
 896     payload_start = offset + 1;
 897     payload_len = len - 1;
 898     if (exception_code != 0) {
 899         proto_item_set_text(mi, "Function %u:  %s.  Exception: %s",
 900                             function_code,
 901                             val_to_str_const(function_code, function_code_vals, "Unknown Function"),
 902                             val_to_str(exception_code,
 903                                        exception_code_vals,
 904                                        "Unknown Exception Code (%u)"));
 905         proto_tree_add_uint(modbus_tree, hf_modbus_exceptioncode, tvb, payload_start, 1,
 906                             exception_code);
 907     }
 908     else {
 909         switch (function_code) {
 910
 911             case READ_COILS:
 912             case READ_DISCRETE_INPUTS:
 913
 914                 if (packet_type == QUERY_PACKET) {
 915                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
 916                     proto_tree_add_item(modbus_tree, hf_modbus_bitcnt, tvb, payload_start + 2, 2, ENC_BIG_ENDIAN);
 917                 }
 918                 else if (packet_type == RESPONSE_PACKET) {
 919                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 920                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1, byte_cnt);
 921                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 1, byte_cnt, register_format);
 922                 }
 923                 break;
 924
 925             case READ_HOLDING_REGS:
 926             case READ_INPUT_REGS:
 927                 if (packet_type == QUERY_PACKET) {
 928                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
 929                     proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, ENC_BIG_ENDIAN);
 930                 }
 931                 else if (packet_type == RESPONSE_PACKET) {
 932                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 933                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1, byte_cnt);
 934                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 1, byte_cnt, register_format);
 935                 }
 936                 break;
 937
 938             case WRITE_SINGLE_COIL:
 939                 if (packet_type == QUERY_PACKET) {
 940                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
 941                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 2, 1, register_format);
 942                     proto_tree_add_text(modbus_tree, tvb, payload_start + 3, 1, "Padding");
 943                 }
 944                 else if (packet_type == RESPONSE_PACKET) {
 945                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
 946                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 2, 1, register_format);
 947                     proto_tree_add_text(modbus_tree, tvb, payload_start + 3, 1, "Padding");
 948                 }
 949                 break;
 950
 951             case WRITE_SINGLE_REG:
 952                 if (packet_type == QUERY_PACKET) {
 953                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
 954                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 2, 2, register_format);
 955                 }
 956                 else if (packet_type == RESPONSE_PACKET) {
 957                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
 958                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 2, 2, register_format);
 959                 }
 960                 break;
 961
 962             case READ_EXCEPT_STAT:
 963                 if (packet_type == RESPONSE_PACKET)
 964                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start, 1, register_format);
 965                 break;
 966
 967             case DIAGNOSTICS:
 968                 if ((packet_type == QUERY_PACKET) || (packet_type == RESPONSE_PACKET)) {
 969                     diagnostic_code = tvb_get_ntohs(tvb, payload_start);
 970                     proto_tree_add_uint(modbus_tree, hf_modbus_diag_sf, tvb, payload_start, 2, diagnostic_code);
 971                     switch(diagnostic_code)
 972                     {
 973                         case RETURN_QUERY_DATA:
 974                             if (packet_type == QUERY_PACKET) {
 975                                 if (payload_len > 2)
 976                                     proto_tree_add_item(modbus_tree, hf_modbus_diag_return_query_data_request, tvb, payload_start+2, payload_len-2, ENC_NA);
 977                             }
 978                             else if (packet_type == RESPONSE_PACKET) {
 979                                 if (payload_len > 2)
 980                                     proto_tree_add_item(modbus_tree, hf_modbus_diag_return_query_data_echo, tvb, payload_start+2, payload_len-2, ENC_NA);
 981                             }
 982                             break;
 983                         case RESTART_COMMUNICATION_OPTION:
 984                             proto_tree_add_item(modbus_tree, hf_modbus_diag_restart_communication_option, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
 985                             break;
 986                         case RETURN_DIAGNOSTIC_REGISTER:
 987                             if (packet_type == QUERY_PACKET) {
 988                                 if (payload_len > 2)
 989                                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
 990                             }
 991                             else if (packet_type == RESPONSE_PACKET) {
 992                                 proto_tree_add_item(modbus_tree, hf_modbus_diag_return_diag_register, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
 993                             }
 994                             break;
 995                         case CHANGE_ASCII_INPUT_DELIMITER:
 996                             proto_tree_add_item(modbus_tree, hf_modbus_diag_ascii_input_delimiter, tvb, payload_start+2, 1, ENC_BIG_ENDIAN);
 997                             break;
 998                         case RETURN_BUS_MESSAGE_COUNT:
 999                             if (packet_type == QUERY_PACKET) {
1000                                 if (payload_len > 2)
1001                                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
1002                             }
1003                             else if (packet_type == RESPONSE_PACKET) {
1004                                 proto_tree_add_item(modbus_tree, hf_modbus_diag_return_bus_message_count, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
1005                             }
1006                             break;
1007                         case RETURN_BUS_COMM_ERROR_COUNT:
1008                             if (packet_type == QUERY_PACKET) {
1009                                 if (payload_len > 2)
1010                                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
1011                             }
1012                             else if (packet_type == RESPONSE_PACKET) {
1013                                 proto_tree_add_item(modbus_tree, hf_modbus_diag_return_bus_comm_error_count, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
1014                             }
1015                             break;
1016                         case RETURN_BUS_EXCEPTION_ERROR_COUNT:
1017                             if (packet_type == QUERY_PACKET) {
1018                                 if (payload_len > 2)
1019                                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
1020                             }
1021                             else if (packet_type == RESPONSE_PACKET) {
1022                                 proto_tree_add_item(modbus_tree, hf_modbus_diag_return_bus_exception_error_count, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
1023                             }
1024                             break;
1025                         case RETURN_SLAVE_MESSAGE_COUNT:
1026                             if (packet_type == QUERY_PACKET) {
1027                                 if (payload_len > 2)
1028                                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
1029                             }
1030                             else if (packet_type == RESPONSE_PACKET) {
1031                                 proto_tree_add_item(modbus_tree, hf_modbus_diag_return_slave_message_count, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
1032                             }
1033                             break;
1034                         case RETURN_SLAVE_NO_RESPONSE_COUNT:
1035                             if (packet_type == QUERY_PACKET) {
1036                                 if (payload_len > 2)
1037                                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
1038                             }
1039                             else if (packet_type == RESPONSE_PACKET) {
1040                                 proto_tree_add_item(modbus_tree, hf_modbus_diag_return_no_slave_response_count, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
1041                             }
1042                             break;
1043                         case RETURN_SLAVE_NAK_COUNT:
1044                             if (packet_type == QUERY_PACKET) {
1045                                 if (payload_len > 2)
1046                                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
1047                             }
1048                             else if (packet_type == RESPONSE_PACKET) {
1049                                 proto_tree_add_item(modbus_tree, hf_modbus_diag_return_slave_nak_count, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
1050                             }
1051                             break;
1052                         case RETURN_SLAVE_BUSY_COUNT:
1053                             if (packet_type == QUERY_PACKET) {
1054                                 if (payload_len > 2)
1055                                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
1056                             }
1057                             else if (packet_type == RESPONSE_PACKET) {
1058                                 proto_tree_add_item(modbus_tree, hf_modbus_diag_return_slave_busy_count, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
1059                             }
1060                             break;
1061                         case RETURN_BUS_CHAR_OVERRUN_COUNT:
1062                             if (packet_type == QUERY_PACKET) {
1063                                 if (payload_len > 2)
1064                                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
1065                             }
1066                             else if (packet_type == RESPONSE_PACKET) {
1067                                 proto_tree_add_item(modbus_tree, hf_modbus_diag_return_bus_char_overrun_count, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
1068                             }
1069                             break;
1070                         case CLEAR_OVERRUN_COUNTER_AND_FLAG:
1071                         case FORCE_LISTEN_ONLY_MODE:
1072                         case CLEAR_COUNTERS_AND_DIAG_REG:
1073                         default:
1074                             if (payload_len > 2)
1075                                 dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start+2, payload_len-2, register_format);
1076                             break;
1077                     }
1078                 }
1079                 break;
1080
1081             case GET_COMM_EVENT_CTRS:
1082                 if (packet_type == RESPONSE_PACKET) {
1083                     proto_tree_add_item(modbus_tree, hf_modbus_status, tvb, payload_start, 2, ENC_BIG_ENDIAN);
1084                     proto_tree_add_item(modbus_tree, hf_modbus_event_count, tvb, payload_start+2, 2, ENC_BIG_ENDIAN);
1085                 }
1086                 break;
1087
1088             case GET_COMM_EVENT_LOG:
1089                 if (packet_type == RESPONSE_PACKET) {
1090                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
1091                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1, byte_cnt);
1092                     proto_tree_add_item(modbus_tree, hf_modbus_status, tvb, payload_start+1, 2, ENC_BIG_ENDIAN);
1093                     proto_tree_add_item(modbus_tree, hf_modbus_event_count, tvb, payload_start+3, 2, ENC_BIG_ENDIAN);
1094                     proto_tree_add_item(modbus_tree, hf_modbus_message_count, tvb, payload_start+5, 2, ENC_BIG_ENDIAN);
1095                     if (byte_cnt-6 > 0) {
1096                         byte_cnt -= 6;
1097                         event_index = 0;
1098                         me = proto_tree_add_text(modbus_tree, tvb, payload_start+7, byte_cnt, "Events");
1099                         event_tree = proto_item_add_subtree(me, ett_events);
1100                         while (byte_cnt > 0) {
1101                             event_code = tvb_get_guint8(tvb, payload_start+7+event_index);
1102                             if (event_code == 0) {
1103                                 proto_tree_add_text(event_tree, tvb, payload_start+7+event_index, 1, "Initiated Communication Restart");
1104                             }
1105                             else if (event_code == 4) {
1106                                 proto_tree_add_text(event_tree, tvb, payload_start+7+event_index, 1, "Entered Listen Only Mode");
1107                             }
1108                             else if (event_code & REMOTE_DEVICE_RECV_EVENT_MASK) {
1109                                 mei = proto_tree_add_text(event_tree, tvb, payload_start+7+event_index, 1, "Receive Event: 0x%02X", event_code);
1110                                 event_item_tree = proto_item_add_subtree(mei, ett_events_recv);
1111
1112                                 /* add subtrees to describe each event bit */
1113                                 proto_tree_add_item(event_item_tree, hf_modbus_event_recv_comm_err,
1114                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1115                                 proto_tree_add_item(event_item_tree, hf_modbus_event_recv_char_over,
1116                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1117                                 proto_tree_add_item(event_item_tree, hf_modbus_event_recv_lo_mode,
1118                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1119                                 proto_tree_add_item(event_item_tree, hf_modbus_event_recv_broadcast,
1120                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1121                             }
1122                             else if ((event_code & REMOTE_DEVICE_SEND_EVENT_MASK) == REMOTE_DEVICE_SEND_EVENT_VALUE) {
1123                                 mei = proto_tree_add_text(event_tree, tvb, payload_start+7+event_index, 1, "Send Event: 0x%02X", event_code);
1124                                 event_item_tree = proto_item_add_subtree(mei, ett_events_send);
1125
1126                                 /* add subtrees to describe each event bit */
1127                                 proto_tree_add_item(event_item_tree, hf_modbus_event_send_read_ex,
1128                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1129                                 proto_tree_add_item(event_item_tree, hf_modbus_event_send_slave_abort_ex,
1130                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1131                                 proto_tree_add_item(event_item_tree, hf_modbus_event_send_slave_busy_ex,
1132                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1133                                 proto_tree_add_item(event_item_tree, hf_modbus_event_send_slave_nak_ex,
1134                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1135                                 proto_tree_add_item(event_item_tree, hf_modbus_event_send_write_timeout,
1136                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1137                                 proto_tree_add_item(event_item_tree, hf_modbus_event_send_lo_mode,
1138                                   tvb, payload_start+7+event_index, 1, ENC_LITTLE_ENDIAN );
1139                             }
1140                             else {
1141                                 proto_tree_add_text(event_tree, tvb, payload_start+7+event_index, 1, "Unknown Event");
1142                             }
1143
1144                             byte_cnt--;
1145                             event_index++;
1146                         }
1147                     }
1148                 }
1149                 break;
1150
1151             case WRITE_MULT_COILS:
1152                 if (packet_type == QUERY_PACKET) {
1153                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
1154                     proto_tree_add_item(modbus_tree, hf_modbus_bitcnt, tvb, payload_start + 2, 2, ENC_BIG_ENDIAN);
1155                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start + 4);
1156                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start + 4, 1,
1157                             byte_cnt);
1158                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 5, byte_cnt, register_format);
1159                 }
1160                 else if (packet_type == RESPONSE_PACKET) {
1161                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
1162                     proto_tree_add_item(modbus_tree, hf_modbus_bitcnt, tvb, payload_start + 2, 2, ENC_BIG_ENDIAN);
1163                 }
1164                 break;
1165
1166             case WRITE_MULT_REGS:
1167                 if (packet_type == QUERY_PACKET) {
1168                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
1169                     proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, ENC_BIG_ENDIAN);
1170                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start + 4);
1171                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start + 4, 1,
1172                             byte_cnt);
1173                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 5, byte_cnt, register_format);
1174                 }
1175                 else if (packet_type == RESPONSE_PACKET) {
1176                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
1177                     proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, ENC_BIG_ENDIAN);
1178                 }
1179                 break;
1180
1181             case READ_FILE_RECORD:
1182                 if (packet_type == QUERY_PACKET) {
1183                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
1184                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
1185                             byte_cnt);
1186
1187                     /* add subtrees to describe each group of packet */
1188                     group_offset = payload_start + 1;
1189                     for (ii = 0; ii < byte_cnt / 7; ii++) {
1190                         mi = proto_tree_add_text( modbus_tree, tvb, group_offset, 7,
1191                                 "Group %u", ii);
1192                         group_tree = proto_item_add_subtree(mi, ett_group_hdr);
1193                         proto_tree_add_item(group_tree, hf_modbus_reftype, tvb, group_offset, 1, ENC_BIG_ENDIAN);
1194                         proto_tree_add_item(group_tree, hf_modbus_lreference, tvb, group_offset + 1, 4, ENC_BIG_ENDIAN);
1195                         proto_tree_add_item(group_tree, hf_modbus_wordcnt, tvb, group_offset + 5, 2, ENC_BIG_ENDIAN);
1196                         group_offset += 7;
1197                     }
1198                 }
1199                 else if (packet_type == RESPONSE_PACKET) {
1200                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
1201                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
1202                             byte_cnt);
1203
1204                     /* add subtrees to describe each group of packet */
1205                     group_offset = payload_start + 1;
1206                     ii = 0;
1207                     while (byte_cnt > 0) {
1208                         group_byte_cnt = (guint32)tvb_get_guint8(tvb, group_offset);
1209                         mi = proto_tree_add_text( modbus_tree, tvb, group_offset, group_byte_cnt + 1,
1210                                 "Group %u", ii);
1211                         group_tree = proto_item_add_subtree(mi, ett_group_hdr);
1212                         proto_tree_add_uint(group_tree, hf_modbus_bytecnt, tvb, group_offset, 1,
1213                                 group_byte_cnt);
1214                         proto_tree_add_item(group_tree, hf_modbus_reftype, tvb, group_offset + 1, 1, ENC_BIG_ENDIAN);
1215                         dissect_modbus_data(tvb, pinfo, group_tree, function_code, group_offset + 2, group_byte_cnt - 1, register_format);
1216                         group_offset += (group_byte_cnt + 1);
1217                         byte_cnt -= (group_byte_cnt + 1);
1218                         ii++;
1219                     }
1220                 }
1221                 break;
1222
1223             case WRITE_FILE_RECORD:
1224                 if ((packet_type == QUERY_PACKET) || (packet_type == RESPONSE_PACKET)) {
1225                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
1226                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
1227                             byte_cnt);
1228
1229                     /* add subtrees to describe each group of packet */
1230                     group_offset = payload_start + 1;
1231                     ii = 0;
1232                     while (byte_cnt > 0) {
1233                         group_word_cnt = tvb_get_ntohs(tvb, group_offset + 5);
1234                         group_byte_cnt = (2 * group_word_cnt) + 7;
1235                         mi = proto_tree_add_text( modbus_tree, tvb, group_offset,
1236                                 group_byte_cnt, "Group %u", ii);
1237                         group_tree = proto_item_add_subtree(mi, ett_group_hdr);
1238                         proto_tree_add_item(group_tree, hf_modbus_reftype, tvb, group_offset, 1, ENC_BIG_ENDIAN);
1239                         proto_tree_add_item(group_tree, hf_modbus_lreference, tvb, group_offset + 1, 4, ENC_BIG_ENDIAN);
1240                         proto_tree_add_uint(group_tree, hf_modbus_wordcnt, tvb, group_offset + 5, 2,
1241                                 group_word_cnt);
1242                         dissect_modbus_data(tvb, pinfo, group_tree, function_code, group_offset + 7, group_byte_cnt - 7, register_format);
1243                         group_offset += group_byte_cnt;
1244                         byte_cnt -= group_byte_cnt;
1245                         ii++;
1246                     }
1247                 }
1248                 break;
1249
1250             case MASK_WRITE_REG:
1251                 if ((packet_type == QUERY_PACKET) || (packet_type == RESPONSE_PACKET)) {
1252                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
1253                     proto_tree_add_item(modbus_tree, hf_modbus_andmask, tvb, payload_start + 2, 2, ENC_BIG_ENDIAN);
1254                     proto_tree_add_item(modbus_tree, hf_modbus_ormask, tvb, payload_start + 4, 2, ENC_BIG_ENDIAN);
1255                 }
1256                 break;
1257
1258             case READ_WRITE_REG:
1259                 if (packet_type == QUERY_PACKET) {
1260                     proto_tree_add_item(modbus_tree, hf_modbus_readref, tvb, payload_start, 2, ENC_BIG_ENDIAN);
1261                     proto_tree_add_item(modbus_tree, hf_modbus_readwordcnt, tvb, payload_start + 2, 2, ENC_BIG_ENDIAN);
1262                     proto_tree_add_item(modbus_tree, hf_modbus_writeref, tvb, payload_start + 4, 2, ENC_BIG_ENDIAN);
1263                     proto_tree_add_item(modbus_tree, hf_modbus_writewordcnt, tvb, payload_start + 6, 2, ENC_BIG_ENDIAN);
1264                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start + 8);
1265                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start + 8, 1,
1266                             byte_cnt);
1267                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 9, byte_cnt, register_format);
1268                 }
1269                 else if (packet_type == RESPONSE_PACKET) {
1270                     byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
1271                     proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
1272                             byte_cnt);
1273                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 1, byte_cnt, register_format);
1274                 }
1275                 break;
1276
1277             case READ_FIFO_QUEUE:
1278                 if (packet_type == QUERY_PACKET)
1279                     proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, ENC_BIG_ENDIAN);
1280                 else if (packet_type == RESPONSE_PACKET) {
1281                     byte_cnt = (guint32)tvb_get_ntohs(tvb, payload_start);
1282                     proto_tree_add_uint(modbus_tree, hf_modbus_lbytecnt, tvb, payload_start, 2,
1283                             byte_cnt);
1284                     proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, ENC_BIG_ENDIAN);
1285                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start + 4, byte_cnt - 2, register_format);
1286                 }
1287                 break;
1288
1289             case ENCAP_INTERFACE_TRANSP:
1290                 if (packet_type == QUERY_PACKET) {
1291                     proto_tree_add_item(modbus_tree, hf_modbus_mei, tvb, payload_start, 1, ENC_BIG_ENDIAN);
1292                     mei_code = tvb_get_guint8(tvb, payload_start);
1293                     switch (mei_code)
1294                     {
1295                         case READ_DEVICE_ID:
1296                             proto_tree_add_item(modbus_tree, hf_modbus_read_device_id, tvb, payload_start+1, 1, ENC_BIG_ENDIAN);
1297                             proto_tree_add_item(modbus_tree, hf_modbus_object_id, tvb, payload_start+2, 1, ENC_BIG_ENDIAN);
1298                             break;
1299
1300                         case CANOPEN_REQ_RESP:
1301                             /* CANopen protocol not part of the Modbus/TCP specification */
1302                         default:
1303                             if (payload_len > 1)
1304                                 dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start, payload_len-1, register_format);
1305                                 break;
1306                     }
1307                 }
1308                 else if (packet_type == RESPONSE_PACKET) {
1309                     proto_tree_add_item(modbus_tree, hf_modbus_mei, tvb, payload_start, 1, ENC_BIG_ENDIAN);
1310                     mei_code = tvb_get_guint8(tvb, payload_start);
1311                     switch (mei_code)
1312                     {
1313                         case READ_DEVICE_ID:
1314                             proto_tree_add_item(modbus_tree, hf_modbus_read_device_id, tvb, payload_start+1, 1, ENC_BIG_ENDIAN);
1315                             proto_tree_add_item(modbus_tree, hf_modbus_conformity_level, tvb, payload_start+2, 1, ENC_BIG_ENDIAN);
1316                             proto_tree_add_item(modbus_tree, hf_modbus_more_follows, tvb, payload_start+3, 1, ENC_BIG_ENDIAN);
1317                             proto_tree_add_item(modbus_tree, hf_modbus_next_object_id, tvb, payload_start+4, 1, ENC_BIG_ENDIAN);
1318                             num_objects = tvb_get_guint8(tvb, payload_start+5);
1319                             proto_tree_add_uint(modbus_tree, hf_modbus_num_objects, tvb, payload_start+5, 1, num_objects);
1320                             doe = proto_tree_add_text(modbus_tree, tvb, payload_start+6, payload_len-6, "Objects");
1321
1322                             object_index = 0;
1323                             for (ii = 0; ii < num_objects; ii++)
1324                             {
1325                                 device_objects_tree = proto_item_add_subtree(doe, ett_device_id_objects);
1326
1327                                 /* add each "object item" as its own subtree */
1328
1329                                 /* compute length of object */
1330                                 object_type = tvb_get_guint8(tvb, payload_start+6+object_index);
1331                                 object_len = tvb_get_guint8(tvb, payload_start+6+object_index+1);
1332
1333                                 doie = proto_tree_add_text(device_objects_tree, tvb, payload_start+6+object_index, 2+object_len, "Object #%d", ii+1);
1334                                 device_objects_item_tree = proto_item_add_subtree(doie, ett_device_id_object_items);
1335
1336                                 proto_tree_add_item(device_objects_item_tree, hf_modbus_object_id, tvb, payload_start+6+object_index, 1, ENC_BIG_ENDIAN);
1337                                 object_index++;
1338
1339                                 proto_tree_add_uint(device_objects_item_tree, hf_modbus_list_object_len, tvb, payload_start+6+object_index, 1, object_len);
1340                                 object_index++;
1341
1342                                 if (object_type < 7)
1343                                 {
1344                                     proto_tree_add_item(device_objects_item_tree, hf_modbus_object_str_value, tvb, payload_start+6+object_index, object_len, ENC_ASCII|ENC_NA);
1345                                 }
1346                                 else
1347                                 {
1348                                     if (object_len > 0)
1349                                         proto_tree_add_text(device_objects_item_tree, tvb, payload_start+6+object_index, object_len, "Object Value");
1350                                 }
1351                                 object_index += object_len;
1352                             }
1353                             break;
1354
1355                         case CANOPEN_REQ_RESP:
1356                             /* CANopen protocol not part of the Modbus/TCP specification */
1357                         default:
1358                             if (payload_len > 1)
1359                                 dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start, payload_len-1, register_format);
1360                                 break;
1361                     }
1362                 }
1363                 break;
1364
1365             case REPORT_SLAVE_ID:
1366             default:
1367                 if (payload_len > 0)
1368                     dissect_modbus_data(tvb, pinfo, modbus_tree, function_code, payload_start, payload_len, register_format);
1369                 break;
1370         }
1371     }
1372
1373     return tvb_length(tvb);
1374 }
1375
1376
1377 /* Register the protocol with Wireshark */
1378
1379 void proto_reg_handoff_mbtcp(void);
1380 void proto_reg_handoff_mbrtu(void);
1381
1382 void
1383 proto_register_modbus(void)
1384 {
1385     /* Modbus/TCP header fields */
1386     static hf_register_info mbtcp_hf[] = {
1387         { &hf_mbtcp_transid,
1388             { "Transaction Identifier",        "mbtcp.trans_id",
1389             FT_UINT16, BASE_DEC, NULL, 0x0,
1390             NULL, HFILL }
1391         },
1392         { &hf_mbtcp_protid,
1393             { "Protocol Identifier",           "mbtcp.prot_id",
1394             FT_UINT16, BASE_DEC, NULL, 0x0,
1395             NULL, HFILL }
1396         },
1397         { &hf_mbtcp_len,
1398             { "Length",                        "mbtcp.len",
1399             FT_UINT16, BASE_DEC, NULL, 0x0,
1400             NULL, HFILL }
1401         },
1402         { &hf_mbtcp_unitid,
1403             { "Unit Identifier",               "mbtcp.unit_id",
1404             FT_UINT8, BASE_DEC, NULL, 0x0,
1405             NULL, HFILL }
1406         },
1407     };
1408
1409     static hf_register_info mbrtu_hf[] = {
1410         { &hf_mbrtu_unitid,
1411             { "Unit ID",                       "mbrtu.unit_id",
1412             FT_UINT8, BASE_DEC, NULL, 0x0,
1413             NULL, HFILL }
1414         },
1415         { &hf_mbrtu_crc16,
1416             { "CRC-16",                        "mbrtu.crc16",
1417             FT_UINT16, BASE_HEX, NULL, 0x0,
1418             NULL, HFILL }
1419         },
1420     };
1421
1422     static ei_register_info mbrtu_ei[] = {
1423         { &ei_mbrtu_crc16_incorrect, { "mbrtu.crc16.incorrect", PI_CHECKSUM, PI_WARN, "Incorrect CRC", EXPFILL }},
1424     };
1425
1426     static hf_register_info hf[] = {
1427         /* Modbus header fields */
1428         { &hf_mbtcp_functioncode,
1429             { "Function Code",                 "modbus.func_code",
1430             FT_UINT8, BASE_DEC, VALS(function_code_vals), 0x0,
1431             NULL, HFILL }
1432         },
1433         { &hf_modbus_reference,
1434             { "Reference Number",              "modbus.reference_num",
1435             FT_UINT16, BASE_DEC, NULL, 0x0,
1436             NULL, HFILL }
1437         },
1438         { &hf_modbus_lreference,
1439             { "Reference Number (32 bit)",     "modbus.reference_num_32",
1440             FT_UINT32, BASE_DEC, NULL, 0x0,
1441             NULL, HFILL }
1442         },
1443         { &hf_modbus_reftype,
1444             { "Reference Type",                "modbus.reference_type",
1445             FT_UINT8, BASE_DEC, NULL, 0x0,
1446             NULL, HFILL }
1447         },
1448         { &hf_modbus_readref,
1449             { "Read Reference Number",         "modbus.read_reference_num",
1450             FT_UINT16, BASE_DEC, NULL, 0x0,
1451             NULL, HFILL }
1452         },
1453         { &hf_modbus_writeref,
1454             { "Write Reference Number",        "modbus.write_reference_num",
1455             FT_UINT16, BASE_DEC, NULL, 0x0,
1456             NULL, HFILL }
1457         },
1458         { &hf_modbus_wordcnt,
1459             { "Word Count",                    "modbus.word_cnt",
1460             FT_UINT16, BASE_DEC, NULL, 0x0,
1461             NULL, HFILL }
1462         },
1463         { &hf_modbus_readwordcnt,
1464             { "Read Word Count",               "modbus.read_word_cnt",
1465             FT_UINT16, BASE_DEC, NULL, 0x0,
1466             NULL, HFILL }
1467         },
1468         { &hf_modbus_writewordcnt,
1469             { "Write Word Count",              "modbus.write_word_cnt",
1470             FT_UINT16, BASE_DEC, NULL, 0x0,
1471             NULL, HFILL }
1472         },
1473         { &hf_modbus_bitcnt,
1474             { "Bit Count",                     "modbus.bit_cnt",
1475             FT_UINT16, BASE_DEC, NULL, 0x0,
1476             NULL, HFILL }
1477         },
1478         { &hf_modbus_bytecnt,
1479             { "Byte Count",                    "modbus.byte_cnt",
1480             FT_UINT8, BASE_DEC, NULL, 0x0,
1481             NULL, HFILL }
1482         },
1483         { &hf_modbus_lbytecnt,
1484             { "Byte Count (16-bit)",           "modbus.byte_cnt_16",
1485             FT_UINT8, BASE_DEC, NULL, 0x0,
1486             NULL, HFILL }
1487         },
1488         { &hf_modbus_exceptioncode,
1489             { "Exception Code",                "modbus.exception_code",
1490             FT_UINT8, BASE_DEC, VALS(exception_code_vals), 0x0,
1491             NULL, HFILL }
1492         },
1493         { &hf_modbus_diag_sf,
1494             { "Diagnostic Code",               "modbus.diagnostic_code",
1495             FT_UINT16, BASE_DEC, VALS(diagnostic_code_vals), 0x0,
1496             NULL, HFILL }
1497         },
1498         { &hf_modbus_diag_return_query_data_request,
1499             { "Request Data",                  "modbus.diagnostic.return_query_data.request",
1500             FT_BYTES, BASE_NONE, NULL, 0x0,
1501             NULL, HFILL }
1502         },
1503         { &hf_modbus_diag_return_query_data_echo,
1504             { "Echo Data",                  "modbus.diagnostic.return_query_data.echo",
1505             FT_BYTES, BASE_NONE, NULL, 0x0,
1506             NULL, HFILL }
1507         },
1508         { &hf_modbus_diag_restart_communication_option,
1509             { "Restart Communication Option", "modbus.diagnostic.restart_communication_option",
1510             FT_UINT16, BASE_HEX, VALS(diagnostic_restart_communication_option_vals), 0x0,
1511             NULL, HFILL }
1512         },
1513         { &hf_modbus_diag_return_diag_register,
1514             { "Diagnostic Register Contents", "modbus.diagnostic.return_diag_register",
1515             FT_UINT16, BASE_HEX, NULL, 0x0,
1516             NULL, HFILL }
1517         },
1518         { &hf_modbus_diag_ascii_input_delimiter,
1519             { "CHAR", "modbus.diagnostic.ascii_input_delimiter",
1520             FT_UINT8, BASE_HEX, NULL, 0x0,
1521             NULL, HFILL }
1522         },
1523         { &hf_modbus_diag_return_bus_message_count,
1524             { "Total Message Count", "modbus.diagnostic.bus_message_count",
1525             FT_UINT16, BASE_DEC, NULL, 0x0,
1526             NULL, HFILL }
1527         },
1528         { &hf_modbus_diag_return_bus_comm_error_count,
1529             { "CRC Error Count", "modbus.diagnostic.bus_comm_error_count",
1530             FT_UINT16, BASE_DEC, NULL, 0x0,
1531             NULL, HFILL }
1532         },
1533         { &hf_modbus_diag_return_bus_exception_error_count,
1534             { "Exception Error Count", "modbus.diagnostic.bus_exception_error_count",
1535             FT_UINT16, BASE_DEC, NULL, 0x0,
1536             NULL, HFILL }
1537         },
1538         { &hf_modbus_diag_return_slave_message_count,
1539             { "Slave Message Count", "modbus.diagnostic.slave_message_count",
1540             FT_UINT16, BASE_DEC, NULL, 0x0,
1541             NULL, HFILL }
1542         },
1543         { &hf_modbus_diag_return_no_slave_response_count,
1544             { "Slave No Response Count", "modbus.diagnostic.no_slave_response_count",
1545             FT_UINT16, BASE_DEC, NULL, 0x0,
1546             NULL, HFILL }
1547         },
1548         { &hf_modbus_diag_return_slave_nak_count,
1549             { "Slave NAK Count", "modbus.diagnostic.slave_nak_count",
1550             FT_UINT16, BASE_DEC, NULL, 0x0,
1551             NULL, HFILL }
1552         },
1553         { &hf_modbus_diag_return_slave_busy_count,
1554             { "Slave Device Busy Count", "modbus.diagnostic.slave_busy_count",
1555             FT_UINT16, BASE_DEC, NULL, 0x0,
1556             NULL, HFILL }
1557         },
1558         { &hf_modbus_diag_return_bus_char_overrun_count,
1559             { "Slave Character Overrun Count", "modbus.diagnostic.bus_char_overrun_count",
1560             FT_UINT16, BASE_DEC, NULL, 0x0,
1561             NULL, HFILL }
1562         },
1563         { &hf_modbus_status,
1564             { "Status",                        "modbus.ev_status",
1565             FT_UINT16, BASE_HEX, NULL, 0x0,
1566             NULL, HFILL }
1567         },
1568         { &hf_modbus_event_count,
1569             { "Event Vount",                   "modbus.ev_count",
1570             FT_UINT16, BASE_DEC, NULL, 0x0,
1571             NULL, HFILL }
1572         },
1573         { &hf_modbus_message_count,
1574             { "Message Count",                 "modbus.ev_msg_count",
1575             FT_UINT16, BASE_DEC, NULL, 0x0,
1576             NULL, HFILL }
1577         },
1578         { &hf_modbus_event_recv_comm_err,
1579             { "Communication Error",           "modbus.ev_recv_comm_err",
1580             FT_UINT8, BASE_DEC, NULL, 0x02,
1581             NULL, HFILL }
1582         },
1583         { &hf_modbus_event_recv_char_over,
1584             { "Character Overrun",             "modbus.ev_recv_char_over",
1585             FT_UINT8, BASE_DEC, NULL, 0x10,
1586             NULL, HFILL }
1587         },
1588         { &hf_modbus_event_recv_lo_mode,
1589             { "Currently in Listen Only Mode", "modbus.ev_recv_lo_mode",
1590             FT_UINT8, BASE_DEC, NULL, 0x20,
1591             NULL, HFILL }
1592         },
1593         { &hf_modbus_event_recv_broadcast,
1594             { "Broadcast Received",            "modbus.ev_recv_broadcast",
1595             FT_UINT8, BASE_DEC, NULL, 0x40,
1596             NULL, HFILL }
1597         },
1598         { &hf_modbus_event_send_read_ex,
1599             { "Read Exception Sent",            "modbus.ev_send_read_ex",
1600             FT_UINT8, BASE_DEC, NULL, 0x01,
1601             NULL, HFILL }
1602         },
1603         { &hf_modbus_event_send_slave_abort_ex,
1604             { "Slave Abort Exception Sent",     "modbus.ev_send_slave_abort_ex",
1605             FT_UINT8, BASE_DEC, NULL, 0x02,
1606             NULL, HFILL }
1607         },
1608         { &hf_modbus_event_send_slave_busy_ex,
1609             { "Slave Busy Exception Sent",      "modbus.ev_send_slave_busy_ex",
1610             FT_UINT8, BASE_DEC, NULL, 0x04,
1611             NULL, HFILL }
1612         },
1613         { &hf_modbus_event_send_slave_nak_ex,
1614             { "Slave Program NAK Exception Sent", "modbus.ev_send_slave_nak_ex",
1615             FT_UINT8, BASE_DEC, NULL, 0x08,
1616             NULL, HFILL }
1617         },
1618         { &hf_modbus_event_send_write_timeout,
1619             { "Write Timeout Error Occurred",  "modbus.ev_send_write_timeout",
1620             FT_UINT8, BASE_DEC, NULL, 0x10,
1621             NULL, HFILL }
1622         },
1623         { &hf_modbus_event_send_lo_mode,
1624             { "Currently in Listen Only Mode", "modbus.ev_send_lo_mode",
1625             FT_UINT8, BASE_DEC, NULL, 0x20,
1626             NULL, HFILL }
1627         },
1628         { &hf_modbus_andmask,
1629             { "AND mask",                      "modbus.and_mask",
1630             FT_UINT16, BASE_HEX, NULL, 0x0,
1631             NULL, HFILL }
1632         },
1633         { &hf_modbus_ormask,
1634             { "OR mask",                       "modbus.or_mask",
1635             FT_UINT16, BASE_HEX, NULL, 0x0,
1636             NULL, HFILL }
1637         },
1638         { &hf_modbus_data,
1639             { "Data",                          "modbus.data",
1640             FT_BYTES,  BASE_NONE, NULL,    0x0, NULL, HFILL }
1641         },
1642         { &hf_modbus_mei,
1643             { "MEI type",                      "modbus.mei",
1644             FT_UINT8, BASE_DEC, VALS(encap_interface_code_vals), 0x0,
1645             NULL, HFILL }
1646         },
1647         { &hf_modbus_read_device_id,
1648             { "Read Device ID",                "modbus.read_device_id",
1649             FT_UINT8, BASE_DEC, VALS(read_device_id_vals), 0x0,
1650             NULL, HFILL }
1651         },
1652         { &hf_modbus_object_id,
1653             { "Object ID",                     "modbus.object_id",
1654             FT_UINT8, BASE_DEC, VALS(object_id_vals), 0x0,
1655             NULL, HFILL }
1656         },
1657         { &hf_modbus_num_objects,
1658             { "Number of Objects",             "modbus.num_objects",
1659             FT_UINT8, BASE_DEC, NULL, 0x0,
1660             NULL, HFILL }
1661         },
1662         { &hf_modbus_list_object_len,
1663             { "Object length",                 "modbus.objects_len",
1664             FT_UINT8, BASE_DEC, NULL, 0x0,
1665             NULL, HFILL }
1666         },
1667         { &hf_modbus_conformity_level,
1668             { "Conformity Level",              "modbus.conformity_level",
1669             FT_UINT8, BASE_HEX, VALS(conformity_level_vals), 0x0,
1670             NULL, HFILL }
1671         },
1672         { &hf_modbus_more_follows,
1673             { "More Follows",                  "modbus.more_follows",
1674             FT_UINT8, BASE_HEX, NULL, 0x0,
1675             NULL, HFILL }
1676         },
1677         { &hf_modbus_next_object_id,
1678             { "Next Object ID",                "modbus.next_object_id",
1679             FT_UINT8, BASE_DEC, NULL, 0x0,
1680             NULL, HFILL }
1681         },
1682         { &hf_modbus_object_str_value,
1683             { "Object String Value",           "modbus.object_str_value",
1684             FT_STRING, BASE_NONE, NULL, 0x0,
1685             NULL, HFILL }
1686         },
1687         { &hf_modbus_reg_uint16,
1688             { "Register (UINT16)",             "modbus.register.uint16",
1689             FT_UINT16, BASE_DEC, NULL, 0x0,
1690             NULL, HFILL }
1691         },
1692         { &hf_modbus_reg_uint32,
1693             { "Register (UINT32)",             "modbus.register.uint32",
1694             FT_UINT32, BASE_DEC, NULL, 0x0,
1695             NULL, HFILL }
1696         },
1697         { &hf_modbus_reg_ieee_float,
1698             { "Register (IEEE Float)",         "modbus.register.ieee_float",
1699             FT_FLOAT, BASE_NONE, NULL, 0x0,
1700             NULL, HFILL }
1701         },
1702         { &hf_modbus_reg_modicon_float,
1703             { "Register (Modicon Float)",      "modbus.register.modicon_float",
1704             FT_FLOAT, BASE_NONE, NULL, 0x0,
1705             NULL, HFILL }
1706         },
1707     };
1708
1709     /* Setup protocol subtree array */
1710     static gint *ett[] = {
1711         &ett_mbtcp,
1712         &ett_mbrtu,
1713         &ett_modbus_hdr,
1714         &ett_group_hdr,
1715         &ett_events,
1716         &ett_events_recv,
1717         &ett_events_send,
1718         &ett_device_id_objects,
1719         &ett_device_id_object_items
1720     };
1721
1722     static ei_register_info ei[] = {
1723         { &ei_modbus_data_decode, { "modbus.data.decode", PI_PROTOCOL, PI_WARN, "Invalid decoding options, register data not a multiple of 4!", EXPFILL }},
1724     };
1725
1726     module_t *mbtcp_module;
1727     module_t *mbrtu_module;
1728     expert_module_t* expert_mbrtu;
1729     expert_module_t* expert_modbus;
1730
1731     /* Register the protocol name and description */
1732     proto_mbtcp = proto_register_protocol("Modbus/TCP", "Modbus/TCP", "mbtcp");
1733     proto_mbrtu = proto_register_protocol("Modbus RTU", "Modbus RTU", "mbrtu");
1734     proto_modbus = proto_register_protocol("Modbus", "Modbus", "modbus");
1735
1736     /* Registering protocol to be called by another dissector */
1737     modbus_handle = new_register_dissector("modbus", dissect_modbus, proto_modbus);
1738     mbtcp_handle = new_register_dissector("mbtcp", dissect_mbtcp, proto_mbtcp);
1739     mbrtu_handle = new_register_dissector("mbrtu", dissect_mbrtu, proto_mbrtu);
1740
1741     /* Registering subdissectors table */
1742     modbus_data_dissector_table = register_dissector_table("modbus.data", "Modbus Data", FT_STRING, BASE_NONE);
1743     modbus_dissector_table = register_dissector_table("mbtcp.prot_id", "Modbus/TCP protocol identifier", FT_UINT16, BASE_DEC);
1744
1745     /* Required function calls to register the header fields and subtrees used */
1746     proto_register_field_array(proto_mbtcp, mbtcp_hf, array_length(mbtcp_hf));
1747     proto_register_field_array(proto_mbrtu, mbrtu_hf, array_length(mbrtu_hf));
1748     proto_register_field_array(proto_modbus, hf, array_length(hf));
1749     proto_register_subtree_array(ett, array_length(ett));
1750     expert_mbrtu = expert_register_protocol(proto_mbrtu);
1751     expert_register_field_array(expert_mbrtu, mbrtu_ei, array_length(mbrtu_ei));
1752     expert_modbus = expert_register_protocol(proto_modbus);
1753     expert_register_field_array(expert_modbus, ei, array_length(ei));
1754
1755
1756     /* Register required preferences for Modbus Protocol register decoding */
1757     mbtcp_module = prefs_register_protocol(proto_mbtcp, proto_reg_handoff_mbtcp);
1758     mbrtu_module = prefs_register_protocol(proto_mbrtu, proto_reg_handoff_mbrtu);
1759
1760     /* Modbus RTU Preference - Desegment, defaults to TRUE for TCP desegmentation */
1761     prefs_register_bool_preference(mbtcp_module, "desegment",
1762                                   "Desegment all Modbus RTU packets spanning multiple TCP segments",
1763                                   "Whether the Modbus RTU dissector should desegment all messages spanning multiple TCP segments",
1764                                   &mbtcp_desegment);
1765
1766     /* Modbus/TCP Preference - Default TCP Port, allows for "user" port either than 502. */
1767     prefs_register_uint_preference(mbtcp_module, "tcp.port", "Modbus/TCP Port",
1768                        "Set the TCP port for Modbus/TCP packets (if other"
1769                        " than the default of 502)",
1770                        10, &global_mbus_tcp_port);
1771
1772     /* Modbus/TCP Preference - Holding/Input Register format, this allows for deeper dissection of response data */
1773     prefs_register_enum_preference(mbtcp_module, "mbus_register_format",
1774                                     "Holding/Input Register Format",
1775                                     "Register Format",
1776                                     &global_mbus_tcp_register_format,
1777                                     mbus_register_format,
1778                                     TRUE);
1779
1780     /* Modbus/TCP Preference - Register addressing format, this allows for a configurable display option to determine addressing used */
1781     prefs_register_enum_preference(mbtcp_module, "mbus_register_addr_type",
1782                                     "Register Addressing Type",
1783                                     "Register Addressing Type (Raw, Modicon 5 or 6). This option has no effect on the underlying protocol, but changes the register address display format",
1784                                     &global_mbus_tcp_register_addr_type,
1785                                     mbus_register_addr_type,
1786                                     TRUE);
1787
1788     /* Modbus RTU Preference - Desegment, defaults to TRUE for TCP desegmentation */
1789     prefs_register_bool_preference(mbrtu_module, "desegment",
1790                                   "Desegment all Modbus RTU packets spanning multiple TCP segments",
1791                                   "Whether the Modbus RTU dissector should desegment all messages spanning multiple TCP segments",
1792                                   &mbrtu_desegment);
1793
1794     /* Modbus RTU Preference - CRC verification, defaults to FALSE (not do verification)*/
1795     prefs_register_bool_preference(mbrtu_module, "crc_verification",
1796                                   "Validate CRC",
1797                                   "Whether to validate the CRC",
1798                                   &mbrtu_crc);
1799
1800     /* Modbus RTU Preference - Default TCP Port, defaults to zero, allows custom user port. */
1801     prefs_register_uint_preference(mbrtu_module, "tcp.port", "Modbus RTU Port",
1802                        "Set the TCP port for encapsulated Modbus RTU packets",
1803                        10, &global_mbus_rtu_port);
1804
1805     /* Modbus RTU Preference - Holding/Input Register format, this allows for deeper dissection of response data */
1806     prefs_register_enum_preference(mbrtu_module, "mbus_register_format",
1807                                     "Holding/Input Register Format",
1808                                     "Register Format",
1809                                     &global_mbus_rtu_register_format,
1810                                     mbus_register_format,
1811                                     TRUE);
1812
1813     /* Modbus RTU Preference - Register addressing format, this allows for a configurable display option to determine addressing used */
1814     prefs_register_enum_preference(mbrtu_module, "mbus_register_addr_type",
1815                                     "Register Addressing Type",
1816                                     "Register Addressing Type (Raw, Modicon 5 or 6). This option has no effect on the underlying protocol, but changes the register address display format",
1817                                     &global_mbus_rtu_register_addr_type,
1818                                     mbus_register_addr_type,
1819                                     TRUE);
1820
1821 }
1822
1823
1824 /* If this dissector uses sub-dissector registration add a registration routine.
1825    This format is required because a script is used to find these routines and
1826    create the code that calls these routines.
1827  */
1828 void
1829 proto_reg_handoff_mbtcp(void)
1830 {
1831     static unsigned int mbtcp_port;
1832
1833     /* Make sure to use Modbus/TCP Preferences field to determine default TCP port */
1834
1835     if(mbtcp_port != 0 && mbtcp_port != global_mbus_tcp_port){
1836         dissector_delete_uint("tcp.port", mbtcp_port, mbtcp_handle);
1837     }
1838
1839     if(global_mbus_tcp_port != 0 && mbtcp_port != global_mbus_tcp_port) {
1840         dissector_add_uint("tcp.port", global_mbus_tcp_port, mbtcp_handle);
1841     }
1842
1843     mbtcp_port = global_mbus_tcp_port;
1844
1845     dissector_add_uint("mbtcp.prot_id", MODBUS_PROTOCOL_ID, modbus_handle);
1846
1847 }
1848
1849 void
1850 proto_reg_handoff_mbrtu(void)
1851 {
1852     static unsigned int mbrtu_port = 0;
1853
1854     /* Make sure to use Modbus RTU Preferences field to determine default TCP port */
1855
1856     if(mbrtu_port != 0 && mbrtu_port != global_mbus_rtu_port){
1857         dissector_delete_uint("tcp.port", mbrtu_port, mbrtu_handle);
1858     }
1859
1860     if(global_mbus_rtu_port != 0 && mbrtu_port != global_mbus_rtu_port) {
1861         dissector_add_uint("tcp.port", global_mbus_rtu_port, mbrtu_handle);
1862     }
1863
1864     mbrtu_port = global_mbus_rtu_port;
1865
1866     dissector_add_uint("mbtcp.prot_id", MODBUS_PROTOCOL_ID, modbus_handle);
1867
1868 }