Tom, not all radios need to be manually switched into communication mode--I don't know about yours. I found out my two Yaesu HF/VHF rigs needed to be switched into "sync" mode but I know the help files said many radios don't. I found the information in the CHIRP help files, on the web. It took a lot more reading help files than it did time to hook things up.
With any luck someone who owns the same IC2100 that you do will come along and give you a REAL answer.
73 GL! --ken