Function Codes; Message Format; Query Messages; Response Messages - ABB M101 Manual

FU N CT IO N CO D ES
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8. Function Codes

The MOBDUS protocol implemented in MNS Digital Gateway is using the MODBUS standard
function codes (FC). The standard function codes supported are as follows:
Function Code
FC02
FC03
FC04
FC06
FC08
FC16

Table 14 Function Codes

The MNS Digital Gateway is a 'standard MODBUS slave device. The PLC or PCS master
initiates the communication by sending the 'Query Messages' and the MNS Digital Gateway
replies the requested information in 'Response Messages'.

8.1. Message Format

8.1.1. Query Messages

The MODBUS query messages have the standard query structure as below.
• The slave address
• Function code for Read or Write operation
• Start address of the desired information
• Register length or data code to be read
• CRC-Error checking field

8.1.2. Response Messages

The MODBUS query messages have the standard query structure as below.
• The slave address
• Applied function code
• Length of response (byte)
• Requested information/Action performed
• CRC-Error checking field
1TG C 9 0 8 0 0 4 M 0 2 0 1
Function
Read Input Status
Read Holding Registers
Read Input Registers
Preset Single Register
Diagnostics
Pre-set multiple Registers
M E S S AG E FO R M AT
Description
Bit-orientated reading from regis-
ter file
Word-orientated reading from reg-
ister file
Word-orientated reading from reg-
ister file
Writing of a word into register file
Check communication between
master and slave, (loop back)
Write of several successive words
into register file
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