I am new to Allen Bradely PLCs. I am going through the online help in RSLogix500 and RS Linx. The only thing i am missing for the time being is the communication cable.
There are dozens of different ways to communicate with Allen Bradley processors. It depends on the PLC type, communications protocol etc. The most common way is with the DF-1 driver for RS232 communications which uses the 1747-cp3 cable.
Have fun learning and you have come to a good spot to ask questions.