Can the ControlLogix act as MODBUS master? If you want to read from the T100MD+ data memory the host must be able to act as MODBUS master. You also have to ensure that the baud rate, data bit, stop bit and parity settings are the same. The PLC ID and address must also be specified correctly. Due to the number of parameters that is involved in a succesful communication the intial setup is the most important. Once the settings are done correctly you should have no problem doing so.
However, if the ConrolLogix is unable to act as MODBUS master, but only as MODBUS slave, then the PLC should be the one initiating the communication. In that case you need to use the READMODBUS or WRITEMODBUS commands in TBASIC to send out MODBUS messages from the T100MD+ PLC to the external control system.
