Hi,

You are right. Setting bit5 high in the option registers configures your timer to accept external clock to count. You also need to set the TRISA bit 4 to 1 accordingly to set as input.

It has a schmitt trigger input which takes much of the pain interfacing it to real world.

While using it as output please note that it is open drain. So you get low levels and floating. Use a pull-up for logic outputs.

I have never used a 16F84 and really did not care about the differences of the A version. But Microchip does maintain a backward compatibility. Bits unused or reserved in one family may have functions in the upper one.

It would be helpful to know what is your application to share knowledge.

BTW skimask he did mention about the datasheet. Not everybody is smart enough to comprehend the manual (take me for example ). Also there are members of this forum whose native language is not English. Wouldn't it be nice for pro-s like you to actually teach and share knowledge than to give lame pointers. It increases your post count however, if that is a hobby.