LED interfacing with 8051 microcomtroller

Led interfacing with 8051 microcontroller 

8051 microcontroller is a 40 pin IC . it has 4 programmable port. each port has 8 pin so it has total 32 programmable pin which can use as input or output. it is a 8 bit IC so each resister and ALU size is 8 bit.

it can program port wise or pin wise both. it has 4 port named P0, P1,P2,and P3. each port has 8 pin

 named --

P0.0 , P0.1,P0.2, P0.3, P0.4, P0.5, ,P0.6,  P0.7.

P1.0, P1.1.................P1.7.

P2. 0.........................P2.7

P3.0............................P3.7

8051 Microcontroller

 in this m.c . P1,P2,and P3 is internally  pull up(all pin have 1) .and P0 is neither pull up( 1 ) nor pull down( 0 ) .so all the port initially act as input.  

   if we want to connect a Led with a m.c. 2 case is possible. 

case 1. 

       joint led at port P0.

case 2.

      joint led at port P1,P2,or P3.

In   case 1 ,  a external resistance is necessary for pull up

 

IN initial both side on led have equal voltage . when pin P0.0 is low led glow because voltage across led is approx 3 v.  when voltage on pin P0.0 is high led will be off.

 220 ohm resistance drop 2 v voltage and  give 3 v. 

in case 2 -

in this case  no need to external pull up resistance . port pin have initially high voltage label . because it is internally pull high. so  if led connect on Port 1,2,or 3 this type of connection is right.

   if pin P2.0 is low led will glow.otherwise led remain off.

 note---  initial connection

          PIN  20- GND,  (0V )

          PIN 40- VCC,(5 V)

          PIN 9 - RST(pull down)

            pin 31 -(5v)

            pin 18 and 19 - crystal(11.0592 MHZ)