Simple Octal Keyboard using AT89C2051 microcontroller

Experiment Name: Simple Octal Keyboard

Objective of project: To learn how to program a microcontroller using assembly language for interfacing octal keyboard 0-7.

Circuit Diagram:

Components:

● AT89C51 Microcontroller

● Bread  board

● 9V DC battery

● Common Anode 7 segment Display

● Resistors -8.2k

● Transistor BC547(NPN)

● 33pF Ceramic capacitors x 2 

● 11.0592 MHz crystal

● 10μF Electrolytic capacitor

● Push switch

● UM66 musical IC

● Buzzer

● Jumpers

● Connecting wires

● Voltage regulator

Flowchart:

Code:

ORG 00H

                                MOV DPTR, #CACODE

                                MOV P3, #0FFH

                                MOV P1, #7FH

;;all keys are open ?

KYCHK:                 MOV A, P3

                                SETB ACC.6

                                CJNE A, #0FFH, KYCHK

                                CALL DBONC      ;20ms

                                CALL DBONC

;; read key board

KYPUSH: MOV A, P3

                                SETB ACC.6

                                CJNE A, #0FFH, RDKEY

                                SJMP KYPUSH

RDKEY:  CALL DBONC

                                CALL DBONC     

                                CPL A

                                MOV R0, #00H

                               

DETEKT:                RRC A

                                JC KYCODE

                                INC R0

                                SJMP DETEKT

KYCODE:              MOV A, R0

                                MOVC A, @A+DPTR

                                MOV P1, A

                                SJMP KYPUSH

DBONC:                MOV R7, #0FFH

WAIT:    DJNZ R7, WAIT

                                RET

CACODE: DB 40H, 79H, 24H, 30H, 19H, 12H, 78H, 02H ; 0-7

                                END

Brief description of program: 

I. Firstly, load 0-7 digit codes of 7 segment display into data pointer

II. Configure p3 port as input and p1 as 7Fh

III. Move the value of P3 into accumulator and compare whether it is equal to 0FFh

1.  If YES, Read P3 again.
2.  If NO, Read P3 and go to step IV.

IV. Complement accumulator and initialize a counter R0

V. Repetitively right shift carry the accumulator and increment counter until carry is 1.

VI. When carry is 1, retrieve key pressed code from data pointer and show it to segment display.

See the project at https://youtu.be/7_CHX7aCmoc