Despatch Protocol Plus Modbus Communications - Manual (Page 4)

Chromalox Instruments and Controls
A-51643 Rev. 6 10/06/03 iii
5.1 F UNCTION S ET O VERVIEW .......................................................................................................................... 20
5.2 R EGISTER AND I/O F UNCTION S ET D ESCRIPTION FOR P ROTOCOL
TM
P LUS .................................................. 21
5.2.1 [01] Read Outputs ................................................................................................................................. 21
5.2.2 [02] Read Input Discretes ...................................................................................................................... 22
5.2.3 [03] Read Holding Registers (Read Multiple Registers) ....................................................................... 23
5.2.4 [04] Read Input Registers ...................................................................................................................... 24
5.2.5 [06] Write Single Register ..................................................................................................................... 25
5.2.6 [16] Write Multiple Registers ................................................................................................................ 26
5.3 D IAGNOSTICS AND S UPPORT D ESCRIPTION FOR P ROTOCOL
TM
P LUS ........................................................... 28
5.3.1 [08] Diagnostics .................................................................................................................................... 28
5.3.1.1 [08 00] Return Query Data ............................................................................................................................ 28
5.3.1.2 [08 01] Restart Communications Option ....................................................................................................... 29
5.3.1.3 [08 02] Return Diagnostic Register ............................................................................................................... 29
5.3.1.4 [08 04] Force Listen Mode Only ................................................................................................................... 30
5.3.1.5 [08 10] Clear Communication Counters ....................................................................................................... 31
5.3.1.6 [08 12] Return Bus Communication Error Count ......................................................................................... 31
5.3.1.7 [08 13] Return Bus Exception Error Count ................................................................................................... 32
5.3.1.8 [08 14] Return Slave Message Count ............................................................................................................ 32
5.3.1.9 [08 15] Return Slave No Response Count ..................................................................................................... 33
5.3.1.10 [08 18] Return Bus Character Overrun Count ............................................................................................... 33
5.3.2 [17] Report Slave ID.............................................................................................................................. 34
5.4 E XCEPTION R ESPONSE D ESCRIPTION .......................................................................................................... 35
5.4.1 [01] Illegal Function ............................................................................................................................. 36
5.4.2 [02] Illegal Data Address ...................................................................................................................... 36
5.4.3 [03] Illegal Data Value .......................................................................................................................... 36
6 MODBUS PROTOCOL QUICK REFERENCE ........................................................................................... 37
6.1 P ROTOCOL F ORMAT .................................................................................................................................... 37
6.2 RTU T RANSMISSION M ODE ........................................................................................................................ 37
6.2.1 Coding System ....................................................................................................................................... 37
6.2.2 Serial Byte Setup .................................................................................................................................... 37
6.2.3 Error Checking Field ............................................................................................................................. 38
6.2.4 Message Framing .................................................................................................................................. 38
6.3 A DDRESS F IELD .......................................................................................................................................... 38
6.4 F UNCTION F IELD ......................................................................................................................................... 38
6.5 D ATA F IELD ................................................................................................................................................ 39
6.6 E RROR C HECKING F IELD ............................................................................................................................ 39
6.7 F IELD C ONTENTS IN M ODBUS M ESSAGES ................................................................................................... 40