We are unable to communicate with Modicon PLC 984-785E series PLC through laptop having Modsoft ver 2.2, the error comes out "Bad checksum error code 120". Can anybody help us?
You need to provide us some additional information such as the computer make and model, operating system, PLC communication cable pinout and serial port configuration. Modsoft is a DOS based programming package for the Modicon PLC. If you are attempting to use Modsoft running on a newer operating system then it will not be able to gain direct access to the required serial communication port.