Issue
Can multiple Modbus devices be mapped to the same IP address when communicating over TCP/IP?
Product Line
Satchwell BAS & Sigma
Environment
Sigma IC3 Modbus
Cause
This configuration is not documented in the official release notes, leading to uncertainty about its feasibility and implementation.
Resolution
Yes, multiple Modbus devices can be mapped to the same IP address using appropriate configuration in the gateway.txt file. This setup is particularly useful when simulating multiple Modbus devices using tools like ModSim or when interfacing with a gateway that multiplexes device IDs.
Example Configuration
; gateway.txt entries
1,1,3,1,1,0x0001,0,0,1 ;Modsim1 40001
2,1,3,2,1,0x0001,0,0,1 ;Modsim1 40002
3,2,3,1,1,0x0001,0,0,1 ;Modsim2 40001
4,2,3,2,1,0x0001,0,0,1 ;Modsim2 40002
5,3,3,1,1,0x0001,0,0,1 ;Modsim3 40001
6,3,3,2,1,0x0001,0,0,1 ;Modsim3 40002
7,4,3,1,1,0x0001,0,0,1 ;Modsim4 40001
8,4,3,2,1,0x0001,0,0,1 ;Modsim4 40002
; IP_ADDRESS_TABLE
1,10.158.72.254
2,10.158.72.254
3,10.158.72.254
4,10.158.72.254Each entry maps a unique Modbus device number to the same IP address (10.158.72.254) but differentiates them using the device ID and register offset.
Important Notes
- Single Gateway Limitation: IC3 Modbus can only be mapped to a single IP gateway or PC application.
- No Dual Mapping: It is not possible to map to two applications running on the same PC simultaneously.
