Hi Everyone,

1) I am using Quantum CPU 140 434 12A, Which has got two modbus comm ports, with XXMIT EFB and RS-232, i successfully communicate to the modbus device from modbus comm 1, But it is not working with the modbus comm port 2 even if i changed port No. in the XXMIT EFB.

2) i Believe that these modbus comm ports can be used with both electrical media that is RS-232 and RS-485, as in the XXMIT instruction's command register BIT No.3 if i make it to 1 then the mode is RS-485, otherwise RS-232 default 0 (Zero) in that bit.

So i tried it using RS-485 with command register changed to 1 in the Bit No. 3, but unfortunately it is not working at all and giving an error in the status register 129, of course the slave device i'm using supports RS-485 MODBUS.

 

According to the XXMIT documentation it will only work with Port 1.

"Port specifies the communications interface. The only authorized values are the values 1 and 2. Port 2 is only available on the Momentum PLC."

 

Quantum supports only one Modbus Master Port, which is Port1. Port 2 has only slave functionality (XXMIT useless).
Use 174CEV30020 ETH/MB Bridge to get another serial master Port. Or use MB+/MB MUX (NW-BM85-Sxxx) ,which gives you 4 Master port.
Good luck!