The Intel's 8253 and 8254 are programmable interval timers designed to interface with MCU microcontrollers to implement counting and timing and other simple functions.
How the 8253 and 8254 works
One of the big problems solved by these integrated circuits (8253/8254) is the very precise timing functionality compared to those managed in software in microcontrollers.
Each of these circuits contains three 16-bit counting registers. Each register has:
Two input pins: CLK input and GATE input
An output pin: OUT
To start the counting operation, one starts to reload register by a value and on a command register, it starts decrementing the value of that register (countdown timer) until it is equal to zero.
Once the zero value in this register is reached, the circuit generates interrupts on channel (IRQ) which can subsequently be used either by a microcontroller or another electronic stage. the circuit generates a pulse which can subsequently be used either by a microcontroller or another electronic stage.
What’s the difference between 8253 and 8254
The 8254 Timer:
Three PIT channels:
Three Independent 16-Bit Timer Tick Counters
Binary or BCD Counting
Status Read-Back Command
Six Programmable Timer Modes.
Handles Inputs from DC to 10 MHz (with independent frequency dividers)s from DC to 10 MHz (with independent frequency dividers)om DC to 10 MHz
8 MHz 8254
10 MHz 8254-2
The 8253 Timer:
Three PIT channels:
Handles Inputs from DC to 2,6 MHz (with independent frequency dividers)
Three Independent 16-Bit Timer Tick Counters
No Binary or BCD Counting
No Status Read-Back Command
Six Programmable Timer Modes
Block Architecture of 8253 or 8254
Here after we can find the block representation of the hardware architecture of the 8253/8254 chips:
8253 8254 programmable timer interval diagram
Pin Configuration of 8253 or 8254
Here after we can find the pinout of the 8253/8254 chips:
8253 8254 programmable timer interval pin diagram
Operating Modes of 8253 or 8254
The 8253/8254 PIT Timer chip offers a variety of operational modes tailored for precise timing, event counting, and signal generation in microprocessor systems.
Mode 0 – Interrupt On Terminal Count
Mode 1 – Hardware Re-triggerable One-shot
Mode 2 – Rate Generator
Mode 3 – Square Wave Generator
Mode 4 – Software Triggered Strobe
Mode 5 – Hardware Triggered Strobe
Features of 8253 or 8254
Other main functions that can be implemented with these circuits:
Programmable Rate Generator
Periodic Timers
Event Counter
Binary Rate Multiplier
Real Time Clock
Digital One-Shot
Complex Motor Controller
Main Asked Questions about 8253 and 8254
Conclusion
The 8253 or 8254 remain an essential component of timing and system control, providing accuracy, flexibility and reliability in applications that require precise timing and counting.
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