Modbus communication between Alstom Micom Relay and Siemens S7/CP441-2

[jdeom]

Our system configuration is as follows.
a. Siemens S7-400 CPU
b. CP441-2 Modbus master communication module
c. Micom Relay PXX, 24 sets
d. RS-485, Modbus
e. Problem
- 1:1 communication : No problem
- 1:N communication : Data missing or mixing(disturbance)

I'd like to know exact cause and solution(with sample program or technical papers).

Thanks

 

[ZapSib]

my understanding is as follow :

with siemens as master and one micom relay, communication is working.

as soon as you plug a second micom, communication fails.

1/ are all micom with differents modbus adresses ?

2/ are RX/TX not crossed ?

are you able to identify one relay raising the trouble ( I mean, if problem is coming fron the second unit, avoid it and jump from 1st to 3rd)

also, be sure that all relay are under modbus and not other protocol.