Modbus Communications; Introduction; Modbus Functions Supported - Honeywell DCP 50 Product Manual

5

MODBUS COMMUNICATIONS

5.1

INTRODUCTION

This Section specifies the MODBUS communications protocol as implemented on the
Controller Programmer.
Certain restrictions have been imposed upon this implementation:
(i) Baud rates may be set to 1200, 2400, 4800 and 9600 only
(ii) Support for multi-parameter Writes is limited to support of the Multi-word
Write Function (Number 16) but will permit writing of one parameter only per
message
(iii) The multi-parameter Read function supports a maximum of 10 parameters
in one message.
5.2

MODBUS FUNCTIONS SUPPORTED

In the following list, the original Gould MODBUS function names have been used,
followed by the JBUS names in italics, where such an equivalence exists. The
MODBUS Function number follows the names.
A Read Coil Status (Read n Bits)
B Read Holding Registers (Read n Words)
C Force Single Coil (Write 1 Bit)
D Preset Single Register (Write 1 Word)
E Loopback Diagnostic Test
F Preset Multiple Registers (Write n Words)
The instrument will identify itself in reply to a Read Holding Registers message which
enquires the values of parameter numbers 121 & 122, as specified in the CNOMO
documentation, and MODBUS Function 17 (Report Slave ID) will not be supported.
01/02
03/04
05
06
08
16
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