ABB M101 - Function Codes; Message Format

FUNCTION CODES MESSAGE FORMAT
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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 Function Description
FC02 Read Input Status Bit-orientated reading from regis-
ter file
FC03 Read Holding Registers Word-orientated reading from reg-
ister file
FC04 Read Input Registers Word-orientated reading from reg-
ister file
FC06
Preset Single Register
Writing of a word into register file
FC08 Diagnostics Check communication between
master and slave,
(loop back)
FC16 Pre-set multiple Registers Write of several successive words
into register
file
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