franko,

consider yourself using a PIC16F628 since it has TIMER features. It will be a lot more easier since PIC16F84 have limited capabiliities. Another thing, it's a more cost efficient device for compared to other one.

in case you consider it, use can use particularly the TIMER1 feature of the device for it can count up to 1/100th (or better) of a second accuracy.

regards,
yettie