PIF-NUS

The Peripheral Interface, or PIF, is a Sharp SM5 microcontroller on the logic board that does many functions for the Nintendo 64. In addition to managing the Joybus protocol for connected hardware like controllers and memory paks, it also continuously communicates with the CIC copy protection chip in the game cartridge, handles console startup, and manages the Reset button.

https://sites.google.com/site/consoleprotocols/home/techinfo/lowlevel/pif12