LS Industrial Systems XGB Series - MBAP Header Structure; Available Function Code; Frame Structure by Function Code

Chapter 5 Protocols of Various Services
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5.3.3 MBAP Header structure
Classification Size Description Client Server
Transaction
Identifier
2 bytes
MODBUS Request/
Response treatment
Initializing
Response repeatedly if server
responses
2 bytes 0 = MODBUS protocol Initializing
Reproducing it from request frame
if server responses
Protocol Identifier
2 bytes
Frame size except
MBAP
Making (If requested) Server makes it (If it responses)
Unit Identifier 1byte
Classification of unit
which connected to
serial line
Initializing
Reproducing it from request frame
if server responses
[Table 5-11] MBAP Header structure
5.3.4 Available function code
Classification Function Modbus mark
Function Code 01 (0x01) Read output bit Read Coils
Function Code 02 (0x02) Read input bit Read Discrete Inputs
Function Code 03 (0x03) Read output word Read Holding Registers
Function Code 04 (0x04) Read input word Write Input Register
Function Code 05 (0x05) Write output bit Write single Coil
Function Code 15 (0x0F) Continuously write output bit Write Multiple Coils
Function Code 16 (0x10) Continuously write output word Write Multiple Registers
[Table 5-12] Available function code
5.3.5 Frame structure by function code
(1) Function code 0x01: Read Coils
(a) Request
Classification Size Range
Function code 1 byte 0x01
Start address 2 bytes 0x0000 ~ 0xFFFF
Number of coils 2 bytes 0x0001 ~ 0x07D0 (2000 bits)
[Table 5-13] Function code 0x01 request frame
(b) Response
Classification Size Range
Function code 1 byte 0x01
Number of bytes 2 bytes N
Coil status n byte n = N or N + 1
[Table 5-14] Function code 0x01 response frame