PLC, Programmable logic Controller

XG5000 and Mod bus Command

Oh your help and knowledge is really useful. Thanks so much!

Yes, it is Modbus ASCII that I am using. Right now I have both PID and PLC setting to 8-bit character set. So I am going off the standard I guess. Btw if you set to 7, does that mean that, for example, 33 will go as  011 0011? I guess it works cause ASCII only has 4's and 3's as the high portion of the byte...


Regarding the hyperterminal, you mentioned checking the 1000H address. That is a fantastic idea but in their manuals I know also that 1000H is the address of PV. Also, I would require an RS 485 to USB converter to hook up to PC and do it and I don't think I want to get that...

Since the RS 485 is between PLC and PID, right now, I just want to have a way to monitor the communication...but the problem is I do not see anything in the PLC software (XG5000) nor in the manuals regarding where to initiate the communication from or what command/function can be added to the ladder logic so that for example when a switch is triggered the PLC issue a command.

Again I really appreciate your time and consideration.

The problem with the wrong word size (7 vs 8 bits) is how the serial ports on either handle the data words.  It might just work out at 8bits/word.  It's worth a try.

Sorry I can't help you on the PLC specifics, I'm just a generic Modbus guy (HMI, SCADA, OPC mostly).

Modbus, until only recently, has been an option on most PLCs, (now it's standard on only a few of the hundreds of models available), so it isn't surprising that you're not finding information on dealing with Modbus for you particular model.   PLCs have at least one, sometimes multiple serial ports, but whether Modbus functionality is implemented is firmware/hardware based.   

Check with the manufacturer to see what they have to say about Modbus.

Good luck.

Dan

http://smxplc.com/

posted by PLC-boss @ 9:31 AM