The adjunction of a second channel (for the mouse) has forced however to redefine a few status and control bits. Eventually (around the late 80486 and early Pentium time frame) PS/2 style mice became popular, and “PC compatible” controllers have supported dual channels from then on (nominally one keyboard and one mouse).įor the keyboard functions proper, the PS2 and AT controllers are very similar. The AT keyboard controller and its “clones” were not capable of interfacing the new PS/2 mouse. Previously PC and compatible mice were connected to different physical interfaces, including Serial Ports.

With the introduction of the PS/2 series, the main change to the keyboard controller subsystem was its expansion to control both a keyboard and a mouse. To reduce costs, some of the general purpose input/output capabilities of the AT controller was used to control various functions unrelated to the keyboard, including: The 8042 was a powerful micro-controller. The old PPI was not part of the motherboard any more. With the PC-AT, IBM introduced new keyboards (with a new bi-directional protocol) and a new keyboard controller (Intel 8042). The XT controller is 100% obsolete and won't be discussed further in this page. 6.7 Step 7: Determine If There Are 2 ChannelsĪ multi-purpose PPI (Intel 8048, Programmable peripheral interface also used to control other functions, like sound and parity error) controlled the original uni-directional, single channel IBM PC and PC-XT keyboard interface.6.6 Step 6: Perform Controller Self Test.

6.5 Step 5: Set the Controller Configuration Byte.6.2 Step 2: Determine if the PS/2 Controller Exists.

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