I have Patron L207 and I'm trying to establish communication with following external Modbus RTU relay board

I tried this:

mbpoll /dev/extcomm/0/0 -m rtu -a 1 -b 9600 -c 8 -P none

But I get

Read output (holding) register failed: Connection timed out

Any hints on wwhat I am doing wrong? I have no experience with RS485 so I am totally stuck.