This is my first message, and (of course) I´m having some problems...

I was using the PIC 16F870 to do some low freq counting (like 0 to 600Hz), It was very stable. Last week I need more memory, so I get a 16F873A (4k), recompile the program and the counter becomes VERY unstable.

Exists some diference between the 16f870 and 16f873a?

I´m using 20MHz crystal and a function generator (calibrated) to send the pulses to the pic.

Please, I need some help because I´m lost...

PS: sorry for my TERRIBLE english...