984-A120 compact controller


Thread Starter

David Trent

I can not get the PLC to talk to the PC
Modbus error code 199

I have dip switches set for address 12
setting are: 9600 baud, Even parity, RTU mode,
1 stop bit, 8 data bits, and com port 1.

we just purchased this machine "used" and the pc and data cable are what came and worked with the machine.

bob peterson

I am not sure if the parameters you are referring to are on the PC or the PLC, but since you said com1 I would guess it is the PC.

IIRC, there is a switch on the PLC that will set the modbus port parameters to some default. i don't recall off hand what that default is but it's in the manual.

There are all kinds of reasons why they may not be able to communicate. You will have to run them down until you figure out just what the problem is and fix the problem.

The 984-A120 does not have any dip switches.

Is it possible that you have another model?

The Modbus serial defaults on a 984-A120 are 9600,8,E,1 as are all Modicon plcs (some older exceptions), but the address is where I think that you are having the issue.

The mem-dip switch sets that. If in DIP it defaults to address 1, then once programmed and another address has been set in the configuration, then that address will be used in the MEM position.

If you have dip switches then to probably have a 984-A145 or 984-A141. A984-A145 has a MODBUS Plus port (different protocol) and those dip switches set that address. Those addresses are binary plus one, so a setting of 12 on the dips would be address 13.