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How do I add an ACE Modbus slave to a Siemens S7-1200 Modbus master?
In an S7-1200 PLC, the MODBUS RTU protocol is organised in two stages around two functions
MB_COMM_LOAD port configuration of the CM PTP module
The “MB_COMM_LOAD” function block which configures the CM PTP module port for Modbus RTU
Either the baud rate (in our case 9600), type of parity bit,… etc…
MB_MASTER Modbus master communication via the PTP port
The “MB_MASTER” function block which provides Modbus master communication via the PTP port
- MODE : 0:read mode, 1:write mode
- MB_ADDR : address of the slave
- DATA_ADDR : address of the register in the Modbus slave
- DATA-PTR : value to send to the slave
Example for our ACE-1630 Modbus RS232 PLC
CoSH: Enable or disable RS485 communication mode = disabled
C-SL : MODBUS RTU
C-no : Modbus slave address = 1
bPS : data transmission speed = 9600
Len : data bits = 8
Prty : parity bit = None
Stop : stop bit = 1