9CAF is FM/PPM only and 9CAP can be either PPM/PCM(the transmitter) There are a number of differences between the 7 & 9 series radios. The best way would be to browse the owners manual on the futaba site:
http://www.futaba-rc.com/manuals/9c-manual-v1_2.pdf for th 9c and :
http://www.futaba-rc.com/manuals/7c-manual.pdf for the 7c. Lot of educational reading in there and you can burn up your printer if you want to.