Blinking leds with 8255 and 8051(89c51,89c52) microcontroller

Here is a simple project on how to interface 8255 with 8051(89c51) microcontroller. The project demonstrates a simple blinking leds program. Leds are connected to 8255 port A. When the lower four bits of 8255 port A is high the upper four bits are low. Leds connected to upper nibble will remain off and those with lower will glow. After some delay the bits are altered and leds with upper will glow and those with lower will become off. This whole condition is continuously running. Making port A nibbles high and low or leds on and off.

If you are not familiar with 8255 programmable peripheral. Here is good tutorial

8255 PIN OUT AND WORKING DESCRIPTION.

I recommend you to take the tutorial because if you are not familiar with 8255 pin out its working and its initializing. Then its very hard to understand the code below.

The circuit is very easy. Connect port 2 of 8051 with data pins of 8255. Make CS(chip select) and RESET pins of 8255 ground. Connect A0 with port 1 pin 0 of 8051 microcontroller, and A1 with port 1 pin 1. Connect WR(write) pin of 8255 with port 3 pin 6. Connect RD(read) pin of 8255 with port 3 pin 7. The circuit diagram is given below.

8255 interfacing with 8051(89c51,89c52) microcontroller

Coding is very easy if you are fully familiar with 8051(89c51,89c52) series microcontrollers, their programming and the working of 8255 PPI. delay() function is used to generate some delay. In main function I first make port 2 and 3 output. Then i made rd(read)=1. Making rd=1 means I didn’t want to read any thing from 8255. Then I made WR(write)=0 means I want to write anything to 8255. Then i send 0x80 to data pins of 8255 it is my control word. It sets all ports A,B & C of 8255 as output. Then i selected control register because control word is always written in control register. Then in continuous while loop i am making port A nibbles high and low. Which alternatively blinks leds.

P2=0xF0 -> Making upper four nibbles of port A of 8255 high and lower low.
P2=0x0F -> Making lower four nibbles of port A of 8255 high and upper low.

These upper two conditions makes leds to look like blinking. The delays between the conditions are very important. They are used to make leds retain in certain condition for some time for example 0xF0 should retain on port A for some time and then switch to 0x0F. If you dont use delays in these two conditions you will be unable to see leds blinking. The program executes so fast that it becomes so hard to identify whats going on.

You can change the code according to your desire. You can use lcd connected with 8255 to display what ever you want. You an extend your ports by connecting 8255 with 8051(89c51,89c52) microcontroller. Download the project files Code(C++,HEX) compiled in keil u vision-3 and give us your feed back on the project. Write your queries below in the comments section.

Blinking Leds with 8255 and 8051(89c51,89c52) microcontroller