Subject : Embedded Systems Design

Topic : Fundamentals of Embedded System

Difficulty level : Low

• Clock pulses are required any digital systems. Microprocessor embedded system digital system. Some microcontrollers have on chip oscillator circuit and require only a crystal to be connected externally, while some require external oscillator circuit.
• 8051 has an on chip oscillator but needs and external clock to run it.
• The oscillator circuit generates the clock pulses so that all the internal and external operations are synchronized.
• The pins XTAL1 & XTAL2 are used to connect crystal. The Crystal is always connected along with the capacitors as shown in figure.
• 8051 microcontroller are available in market with varying range of operation from 1MHz to 16 MHz
• Generally 11.0592 MHz crystal oscillators are used so that the 8051 microcontroller systems are compatible with the serial port.

• One machine cycle comprises of 12 oscillator periods. Hence to find the time for one machine cycle we need to consider 1/12th of Crystal frequency.