A 20-pin version is made. In my haste, misread your original post that referred to your chip as (-20/P) and assumed you were referring to the number of pins. However, my comments about the program header and linker files I believe are still correct. In my own endeavors, I migrated from the 16F84 to the 16F628A without actually using the 16F628 version. I did need to update my programmer to program the 628A. As to the effect of oscillator frequency on the function, it should have very little effect, except timing loops will need to be adjusted if you use a different frequency. I recommend checking the datasheet for the version you have to determine how the frequency may be set to the same frequency used in the original version by Bigboat.

Sorry for the confusion I caused. John