Date Code 980420
Modbus Plus Message Example
C-1
SEL-2711 Instruction Manual
APPENDIX C: MODBUS PLUS MESSAGE EXAMPLE
This appendix illustrates a common Modbus Plus message. For example, we will have a host read
holding resisters 40540 - 40559 (meter data from port 1 relay). The request message will have the
following structure:
03h
-
function code - read holding register
02h
starting address 539; 40540 starting address less the 40001 base for holding
registers
1Bh
00h
register count - 20; registers 40540 to 40559 inclusive
14h
There are two response messages possible. An error response will have the following format:
83h
-
error function code - error with read holding register
xx
-
error code - value depends on error type
A normal response will have the following format:
03h
-
function code - read holding register
28h
-
byte count 40; number of data bytes in 20 registers
xx
xx
.
data - 40 bytes (20 registers) of data
.
.
xx
