ASCII communications between PC and Modicon 140 CPU 113 02 (Quantum) PLC, using standard settings, fail to get any response.

The message I am sending is:
":0b030000001B98" followed by CR and LF.
(start:station 11:function code 3 - read holding registers: address 0:27 elements:checksum 98)

The station number has been set to 11.

The ASCII/RTU/mem switch is in the "ASCII" position. The communications parameters are: 2400,E,7,1, as dictated by the "ASCII" position.

Using Modicon communications cable, plugged between Com1 and Modbus (not Modbus Plus, which is unconnected).

There is no response from the PLC.

Processor lights "Ready", "Bat low" and flashes "Modbus+". "Modbus" is not illuminated.

Any ideas what I have done wrong?

 

After a quick look I got a LRC (checksum) of d7. Give that a try. Everything else seems OK. It has been a long time since I have done this....

 

The ASCII switch settings are for MODBUS ASCII comms only. Quantum CPU's cannot be used for standard ASCII comms. You must use an ASCII interface module on the Quantum rack. The part number for this is 140ESI06210.