If you want to change from a 877A to something bigger you should consider the 18F4620 since it shares the pinout. Just plug that PIC in the same place as the 877A and adjust the code for the PIC registers and you are up and running. It doesnt hurt either that it has bigger codespace than the 4550 unless USB is the extra feature you are looking for then you have to go for the 4550.


/me