The original IBM PC keyboard used an 8048 as its internal microcontroller. The PC AT replaced the PC's Intel 8255 peripheral interface chip at I/O port addresses with an 8042 accessible through port addresses and . As well as managing the keyboard interface, the 8042 controlled the A20 line gating function for the AT's Intel 80286 CPU and could be commanded by software to reset the 80286 (unlike the 80386 and later processors, the 80286 had no way of switching from protected mode back to real mode except by being reset). Later PC compatibles integrate the 8042's functions into their super I/O devices.