16f877A V 18F4550

[MyBuddy]

I've found many. It would be tedious to list all the pin differences. Basically, don't try to drop this chip into an 877 circuit unless you want to redesign the layout. I'm a beginner, and I found that out the hard way. Bleh.

Here's what got me most:

Port C pins 4 and 5 are digital input ONLY, and on reset they are normally disabled. Unless, that is, the USB module and USB tranciever are disabled.