ok, after killing my last 877a i orderd a new 877a and a 4550...
Acording to microchip, the 877a and the 4550 are not pin compatable...

However, i disagre...
with the following exceptions...

Pin 18:
877a: RC3 (SCK/SCL)
4550: VUSB
i havn't actually used pin 18 yet...

Pin 14:
877a: OSC2 (CLKO)
4550: OSC2 (CLKO/RA6)
oooh, if i use internal clock i get an extra IO pin...

Pin 1:
877a: MCLR (VPP)
4550: MCLR (VPP/RE3)
Question... how the hell can MCLR be used as an IO pin? as soon as it goes low (if input or output) your CPU resets...

I'm aware their is a gneration gap between them...
I'm aware their are internal changes...
I'm aware their are more analog lines
and I'm aware that the 4550 can run upto 48MHz (thats the main reason i baught it!)

Anyone know of any other pin diferences that i've missed?

Thanks