Conventional wisdom states that ISRs should do only minimalistic functions. Never call a subroutine from an interrupt handler. Never use PAUSE type statements. In short, turn something on or off, or set a flag you can poll and service in your main loop. With that said, most ISRs can be crafted in ASM with only basic BSF/BCF and perhaps MOVLW/MOVF type commands. Leave the heavy lifting for a subroutine you write in PBP.