8051_Up-Down Counter

This project shows an Up-Down counter using 8051. The counter is designed to count upto ‘FF’. To simulate circuit in this project, initially activate Mixed Mode simulator from the Schematic Editor window. Simulation can be performed by selecting Run Transient analysis (Oscillograph) from Simulation menu.

The circuit contains an 8051 chip, Interrupt Pulse Generator , Binary to 7 Segment Decoder and Seven Segment LED Display. The Interrupt Pulse Generator is connected to the INT0 pin of 8051. In this circuit Port P2 is set as the output port. The counter is internally set through the code to count in the ascending mode. But when an interrupt pulse is received at the INT0 pin, the counter counts in the descending mode upto zero and continues with the ascending mode. The count sequence appears at the LED display in 7-segment form.

The source code written either in C or Assembly language can be viewed from the code editor window

The program is as shown:

main:

setb EA ; EA is set to enable all interrupts

setb EX0 ; EX0 is set to enable External Interrupt 0

mov a, #0x00 ; Accumulator is loaded with value ‘00’

mov r0,#0xFF ; An internal counter is set to count upto ‘FF’

mov TMOD,#0x00 ; 13-bit timer mode is set.

mov TH0, #0xff ; To get the required time delay, set T0 as ‘FFDF’

mov TL0, #0xdf

loop2:

mov p2,a ; Value in Accumulator is copied to Port P2

clr p3.0 ; P3.0 is cleared to enable decoder

setb TR0 ; TR0 is set to value ‘1’ to start the Timer 0

delay:

jnb TF0, delay ; Checking whether TF0 is set to value ‘1’

inc a ; Incrementing the content of Accumulator

djnz r0,loop2 ; Check whether r0 is zero. If not, jump to loop2

clr TR0 ; Set value of TR0 to’0’ to stop the Timer 0

clr TF0 ; Set value of TF0 to ‘0’

reti ; Return function

; function int_t0

_int_t0:

push acc ; Pushing the contents of Accumulator, register B, Data Pointer and Program Status Word to Stack

push b

push dpl

push dph

push psw

mov psw,#0x00 ; The value ‘00’ is copied to PSW.

mov TH1, #0xff ; To get the required time delay, set T1 as ‘FFDF’

mov TL1, #0xdf

loop3:

mov p2,a ; The content of Accumulator is copied to Port P2

clr p3.0 ; P3.0 is cleared to enable decoder

del:

setb TR1 ; TR1 is set to value ‘1’ to start Timer 1

delay2:

jnb TF1,delay2 ; Checking whether TF1 is set to value ‘1’

clr TR1 ; Set value of TR1 to’0’ to stop Timer 1

clr TF1 ; Set value of TF1 to’0’

dec a ; Decrement Accumulator content

jnz loop3 ; Check whether Accumulator content is zero. If not, jump to loop3

pop psw ; Popping the contents of Accumulator, register B, Data Pointer and Program Status Word from Stack

pop dph

pop dpl

pop b

pop acc

sjmp main ; Jump to main

The source code in the code editor window has to be compiled after making any modifications

(editing). Also the code can be debugged during simulation.