8253 Microprocessor Quiz and Flashcards: 8253/54 Study Guide

Study Notes

PIT is used to generate lower frequencies for various applications, such as producing a beep sound.
Compatible with all Intel and most other microprocessors.
Designed as a microcomputer peripheral to solve common timing control problems.

Measure time delays between external events.
Count the number of times an event occurs.
Cause the processor to be interrupted after a programmed number of external events.
Real-time clock.

3 independent 16-bit down counters, each working independently and programmable separately.
Counters can be programmed in 6 different modes, all software programmable.
Counting facility in both BCD and Binary number systems.
READ BACK COMMAND allows checking the count value, programmed mode, and current status of the counter.

6 modes of operation, with differences in "OUT" signal shape, periodic or non-periodic, and triggering/start of the counter.
Mode 0: Interrupt on Terminal Count, output goes high when count reaches zero.
Mode 1: Programmable One-Shot, output goes low following the rising edge of the gate input.
Mode 2: Rate Generator, counter continually counts down and output pulses low when count reaches zero.
Mode 3: Square Wave Generator, output remains low for half of the timer period and high for the other half.
Mode 4: Software Triggered Strobe, output remains high until timer counts to zero and then pulses low.

Data bus (D0-D7): 8-bit bi-directional buses for transferring data.
VCC and GND: +5V power supply and 0V.
CS (Chip Select): enables communication between 8253/54 and CPU.
RD (Read): enables 8253/54 to send data or status information to CPU.
WR (Write): enables CPU to write data or control words into 8253/54.
A0 and A1: select counters and control word register.
CLK: input clock frequency, ranging from 0 to 2 MHz for 8253.
OUT: can have square-wave, one-shot, and other square-shape waves for various duty cycles.
Gate: enables or disables the counter (HIGH = 5V, LOW = 0V).