I am new to PIC stuff, and have made a few projects (successfully) using PIC16F84.
I have been writing code for new projects, but as the 16F84 is obsolete, what chip can I use as a replacement and what changes, if any, have to be made to the code?
Aside from setting the __CONFIG differently usually just turning off the comparators will make it very similar to the 16F84 and you get the 4MHz clock built in!
I cut my PIC teeth on the old 16C54, such a simple chip and still very powerful. Having only 7 SFRs not too intimidating. The true king of the 18pin 16f series is the 16f88, it's a lot more complex than the f84 for sure but its an awesome little pic, second to that the 16f628a.
if you're just getting started with pics try the free MPLAB simulator. Nothing to build, it's got all the PIC simulators and you can try your hand at some coding right away.