Intel 8253

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The Intel 8253 and 8254 are programmable interval timers (PITs), which perform timing and counting functions using three 16-bit counters.^[1]

The 825x family was primarily designed for the Intel 8080/8085-processors, but were later used in x86 compatible systems. The 825x chips, or an equivalent circuit embedded in a larger chip, are found in all IBM PC compatibles and Soviet computers like the Vector-06C.

In PC compatibles, Timer Channel 0 is assigned to IRQ-0 (the highest priority hardware interrupt). Timer Channel 1 is assigned to DRAM refresh (at least in early models before the 80386). Timer Channel 2 is assigned to the PC speaker.

The Intel 82c54 (c for CMOS logic) variant handles up to 10 MHz clock signals.^[1]