PLC No Response

[kparson]

Have a T100MD888, Trying to connect an MMI-6050 via RS485.  Using MODBUS ASCII.  Was getting PLC no response showing up regularly.  Used SETSYTEM 3,0 and now have no connection at all.  Tried SETSYSTEM 3,1, still no connection.  HELP!

[support]

You mean now you have no connection with the PLC? You may need to turn on DIP switch #4 and reset the PLC, change baud rate to 9600 bps and then try to transfer a blank program to the PLC. Once you have cleared the program that is interfering with your TLServer communication, turn off DIP switch #4, reset PLC and change TLServer to 38.400 bps again.

Troubleshooting ASCII modbus - make sure that the baud rate settings of the PLC match that of your HMI. The default is 38,400, 8, 1, n.

Since you are using Modbus ASCII, you can run a HyperTerminal program on a PC and try to tap the communication between the HMI and the PLC. You can see if the HMI is sending out the command correctly and the response that PLC send back. You will have better idea of where goes wrong. Most likely the HMI is not really sending out Modbus ASCII messages or is not set to the correct baud rate. Please check.

[kparson]

Thanks for the reply.  I was able to solve the problem by increasing the turn around delay on the MMI to 30ms.