Module 5 : Experiments on Microcontrollers

Lecture 39 : Blinking  of LED using AT89C51


To blink an LED connected to one of the port pin (say P 1.0) continuously.


  1. Atmel 89C51 micro controller
  2. 8051 simulator - win8051
  3. Universal SP3 Programmer
  4. Software to load the code into Universal SP3 Programmer
  5. Computer System with Windows 98 or later operating system and RS 232 Cable
  6. +5V D.C Power Supply
  7. Resistors-8.2k-1,1k-1
  8. Capacitors-30pF-2, 10uF-1
  9. 10MHz crystal
  10. LED-1
  11. SPST switches-1
  1. Write the assembly code in win8051 simulator , compile it and check for errors
  2. Once the code is error free, run it and check the output in the simulator.
  3. After checking the code in the simulator, load the code (in .HEX format) into Atmel 89C51 microcontroller using Universal SP3 Programmer.
  4. Make connections as shown in the circuit diagram.
  5. Switch on the power supply and observe the blinking of LED.
  6. Now decrease the delay time in the code and observe the increase in blinking rate.



If we decrease the delay loop time to a very small value, we cannot observe the blinking so try to increase the delay loop time if blinking of LED is not visible.


Successfully completed the blinking of LED using Atmel 89c51 microcontroller.

Circuit Diagram:

Fig 39.1 Circuit diagram for blinking LED experiment

Fig 39.2  Circuit asembly with breadboard