The SCADApack is a Canadian PLC with some integrated analog and digital I/O onboard. It talks standard Modbus. However, right out of the box, it isn't ready to do any talking. At minimum, to establish communications, you must assign addresses to the I/O registers and configure and download some kind of 'dummy' program consisting of at least one rung of ladder logic. This is done via their TelePACE Ladder Logic Editor program for Windows.

For example, you would assign the addresses to conform to Modbus conventions:

digital inputs 10001-1xxxx
digital outputs 00001-0xxxx
analog inputs 30001-3xxxx
analog outputs 40001-4xxxx

Then, configure one rung of logic, i.e. input 10001 directly controlling output 00001. Once this data is downloaded to the PLC and executed, it's ready to talk RS232 via null-modem cable to your PC's COM port.

On the Citect end of things, setup is very straightforward:

1. Set up a COMx type Board and Port as normal.
2. Configure an I/O device using MODBUS protocol, 9600 baud, 8 data bits, 1 stop bit, no parity.
3. Everything should be ready to go.