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THE PROGRAMMABLE INTERVAL TIMER

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• Programmable interval timer/counter

• Includes three independent 16-bit counters

• Has six modes of operation

• Operation:-– A 16-bit count is loaded on the counter and on

command it starts decrement– When the count reaches zero it generates a

pulse

8254 Block Diagram

8254 Control Word Format

Mode 0: Interrupt on Terminal Count

Mode 1 : Programmable One-Shot

Mode 2 : Rate Generator Clock

Mode 3: Square Wave Generator

Mode 4: Software Triggered Strobe

Mode 5: Hardware Triggered Strobe

Read-Back Command Format

Status Byte