Assembly Language Programs
SUBJECT : Microcontrollers and Applications
AUTHOR : Trupti Patil and Prashant Bachanna
PUBLISHED ON : 03/04/18
NUMBER OF PAGES : ( 15 Pages)
PRICE : Rs 9.75

The CPU takes a certain number of clock cycles to execute an instruction. In the 8051 family, these clock cycles are referred to as machine cycles. Table A-l provides the list of 8051 instructions and their machine cycles. To calculate a time delay, we use this list. In the 8051 family, the length of the machine cycle depends on the frequency of the crystal oscillator connected to the 8051 system. The crystal oscillator, along with on-chip circuitry, provide the clock source for the 8051 CPU (see Chapter 8). The frequency of the crystal connected to the 8051 family can vary from 4 MHz to 30 MHz, depending on the chip rating and manufacturer. Very often the 11.0592 MHz crystal oscillator is used to make the 8051 -based system compatible with the serial port of the IBM PC (see Chapter 10). In the original 8051, one machine cycle lasts 12 oscillator periods. Therefore, to calculate the machine cycle for the 8051, we take 1/12 of the crystal frequency, then take its inverse.