Learning the Basics of Timers in 8051 Microcontroller: A Comprehensive Guide

To understand the concept of timers in the 8051 microcontroller and to program effectively, you'll need a solid foundation. This guide will help you navigate through the basics, the programming aspects, and useful resources. Whether you're a student or a professional, a good understanding of the 8051 timers is crucial for many applications, from embedded systems to timing control in various devices. Let's dive into the details.

Understanding the Concept

The first step in learning about timers in the 8051 microcontroller involves understanding the machine cycle (M.C.). The M.C. is the basic unit of time for execution of instructions in the CPU. It is defined as the time taken for one execution cycle. For the AT89S51/2 microcontroller, let's assume the crystal frequency (Fcpu) is 12 MHz.

Calculating Machine Cycle

The machine cycle for the 8051 microcontroller can be calculated using the formula:

To calculate the machine cycle:

M.C. 12 / Fcpu

Assuming Fcpu 12 MHz (12 million cycles per second),

M.C. 12 / 12,000,000 1 microsecond.

Since the same clock is provided to the timer, the timer runs on the same frequency, which is 1 MHz in this case.

Types of Timers

The 8051 microcontroller has two timers: Timer 0 and Timer 1. Both timers are 8-bit timers by default, but Timer 1 can be extended to 16-bit by using Timer 0 as the low byte. Timers can count up to 2n-1 where n is the number of bits in the timer. In the case of an 8-bit timer, the maximum count is 255 (28-1).

Timer Overflow

When a timer overflows (i.e., the count reaches 255 for Timer 0 or 65535 for Timer 1 in 16-bit mode), it generates an overflow flag. This flag can be checked using:

Polling: A loop in the program checks the flag status periodically. Interrupt: The microcontroller can be set up to trigger a subroutine when the overflow flag is raised, which is more efficient and allows the processor to continue with other tasks.

Resources for Learning

To get a detailed understanding of the 8051 microcontroller, including its timers, you may refer to the datasheet of 89V51RD2 or similar models available from NXP. The datasheet provides comprehensive information on all features and registers of the 8051 microcontroller.

For students, the books by Ayala and Mazidi are excellent resources. Microcontroller Fundamentals: Programming and Hardware Design Using 8051 and 8032 by Richard C. Ayala and Building Embedded Systems with the 8051 Microcontroller by Muhammad Ali Mazidi are well-regarded texts that offer detailed coverage of 8051 programming and hardware design.

If you are not a student, consider whether the 8051 microcontroller is the best choice for your project. Modern alternatives like AVR or ARM microcontrollers offer superior performance and are often easier to work with, especially for more advanced projects.