MCS-51 Clock

Introduction:

In this project, I started to learn the MCS-51 assembly language from my dad. First, I learned some basic MCS-51 instructions, such as "MOV", "INC", "CLR C", and "SUBB". I made a simple 7-segment display digit with machine code programming. Then, I started writing code in assembly language. The development environment used was MIDE-51, an open source program under Windows 10. HEX code can be downloaded to wire-wrap an 89C52 prototype. The download function on PC is implemented with Tera Term's "Macro 'file send'". The first assembly code I wrote was for a clock, displaying HH:MM:SS on Tera Term. The code diagram, source code, and the result are shown below.

Pre-Clock Work

After my dad and I were done with the first project, I took off all the wires, except the switch and the single LED were kept, and put on new ones for our second project. The installment of the new wires has been recorded in the following schematic.

The second project is a MCS-51 microprocessor hardware system, and I wired the prototype. After the wiring was done, I connected the board to Tera Term and type the machine code on Tera Term. I began with the basics, using machine code to display a numbers (0, 1, 2, 3, etc.) on our LED 7-Segment display. Shortly, I found that machine code is extremely hard to memorize. Therefore, I started to learn assembly language from my dad, which represents the machine code with a string of letters and numbers (instruction). With the MCS-51 assembly language, I began writing code and using it to debug the MCS-51 prototype. The development environment was MIDE-51 (open source program).

The Board

This is the board I made (front view). The LED display is no longer used, as I've begun to use Tera Term as the code-displayer.

The Back of the Board

This is the same board (back view). I took off all the previous wires and installed new ones in its place.

After Machine Code

After I was done with writing machine code on Tera Term, I switched to MCS-51 assembly language, which was written on MIDE-51. I slowly progressed towards making the clock: in the process, my dad and I also made some mini projects that would aide our advancement in the understanding of assembly language.

I also wrote a code on MIDE-51 that would display a counting-up sequence on the LED 7-segment display. The 7-segment LED digit is driven by Port1(7....0)= NOT (a,b,c,d,e,f,g,PD). The code for it is below -->

code for counting up 2 (click to view)

org 0000h

here1: mov R7,#0

mov 30H,R7

here5: lcall display

lcall Delay2s

inc R7

mov a,r7

clr c

SUBB a,#0fh ; count to this number, 02h-10h

JZ here1 ; if R7 reaches 12, then R7 =0 if (R7==0xc

ljmp here5

;here1: mov R7,#0

; ljmp here5

org 0100h

DB 03H ;”0”

db 9FH

db 25H

db 0DH

db 99H

db 49H

db 41H

db 1FH

db 01H

db 19H

db 11H

db 0C1H

db 63H

db 85H

db 61H

db 71H

;”F”

org 0200H

Display: MOV DPTR,#0100h ; #0100 is the start address where we put the digit BYTE

MOV A,R7

MOVC A,@A+DPTR ; Look up the digit BYTE table to A

MOV P1,A ; display number on 7 segment LED diplay

RET

org 0300H

;setb P1.0

;clr p1.6

Delay2s: mov r3,#20H

here3: mov r2,#0

here2: mov r1,#0

here: djnz r1,here

djnz R2,here2

djnz r3,here3

ret

;clr p1.7

;here9: sjmp here9

END

As shown above, I also learned some of the ASCII table, which I used in the code.

full code for the clock (click to view)

org 0000h

mov 40h,#0 ;clear buffer

mov 41h,#0

mov 42h,#0

mov 43h,#0

mov 44h,#0

mov 45h,#0

;step 2 Display inital 00:00:00 of your buffer 40H-45H with putchar

step2: lcall kbhit

cjne R7,#0,readKey

; mov a,r7

;clr c

;subb a,#0

;jz display_nom

sjmp display_nom

;if no key is pressed, go to normal time display. otherwise, read keyboard, accpet numbers, and put into 40H-45H

readKey: mov r0,#40h

mov r2,#3

loopkey1: mov r3,#2

loopkey: lcall getchar

lcall putchar

mov a,r7

clr c

subb a,#'0'

mov @r0,a

inc r0

djnz r3, loopkey

mov r7,#':'

lcall putchar

djnz R2, loopkey1

mov r7,#0dh

lcall putchar

mov r7, #0ah

lcall putchar

display_nom: lcall disTime

;step 3 ;Delay 1 second

lcall Delay1s

;step 4 Increase 45H by 1 and handle all the carries, display buffers

inc 45H

mov a,45H

clr c

SUBB a,#10 ; xx:xx:x(45H) if (45H)=10, Carry in to (44H), to count from 0 to 9

JNZ next1

inc 44H ;xx:xx:(44H)x

mov 45H,#0

mov a,44H

clr c

SUBB a,#6

JNZ next1

inc 43H

mov a,43H

mov 44H,#0

clr c

SUBB a,#10

JNZ next1

inc 42H

mov 43H,#0

mov a,42H

clr c

SUBB a,#6

JNZ next1

inc 41H

mov 42H,#0

; if 40H=0 go to 41H mode9, else got to 41H mode2

mov a,40H

clr c

subb a,#0

; 40H: 0 41H: 0-9

mov a,41h

jnz mode2

clr c

subb a,#10

sjmp next3

mode2: inc 40H

mov a,40H

mov 41H,0

clr c

subb a,#3

mov a,40H

clr c

subb a,#2

mov 40H,0

jnz next1

next3: inc 40h

mov 41h,#0

mov a,40H

clr c

SUBB a,#2

mov 40h,#0

sjmp next4

next4: mov a,41H

clr c

SUBB a,#3

next1: ljmp step2 ;display_nom

disTime: ; convert number in 40h to 45H to ASCII and display

mov a,40H

add A,#'0'

mov r7,a

lcall putchar

mov a,41H

add a,#'0'

mov r7,a

lcall putchar

mov r7,#':'

lcall putchar

mov a,42H

add a,#'0'

mov r7,a

lcall putchar

mov a,43H

add a,#'0'

mov r7,a

lcall putchar

mov r7,#':'

lcall putchar

mov a,44H

add a,#'0'

mov r7,a

lcall putchar

mov a,45H

add a,#'0'

mov r7,a

lcall putchar

mov r7,#0dh

lcall putchar

mov r7,#0ah

lcall putchar

ret

justinl: lcall putchar;

inc R7

djnz r6,justinl

mov r7,#0ah

lcall putchar;

mov R7,#'A'

lcall putchar;

lcall puts

sjmp $

putchar: jnb ti,$

clr ti

mov sbuf,R7 ;the ASCII to be displayed in R7

ret

getchar: jnb ri,$ ;read char from teraterm and put in R7

mov r7,sbuf

clr ri

ret

kbhit: jnb ri,nokey ;check if key is pressed, if so, return R7=1, otherwise R7=0

mov r7,#1

ret

nokey: mov r7,#0

ret

;----------------------------------------------------

puts: mov dptr, #bufLen

movx A,@DPTR

mov R6,a

mov dptr,#disBuf

movx a, @dptr

mov R7,a

bufLen: db 4

;disBuf: db "abcd", 0ah

disBuf: db "01:23:45",0ah

Delay1s: mov r3,#10H

here3: mov r2,#0

here2: mov r1,#0

here: djnz r1,here

djnz R2,here2

djnz r3,here3

ret

END

Code Diagram

The diagram is shown above. This is the diagram I used to design the code. After drawing and analyzing the code onto this diagram, I was able to dissect the code into smaller pieces and focus on which parts to fix when the code went wrong. This diagram was created by DIA, a program my dad introduced me to that helped with graphs and diagrams.

Code Process

This is the process in which I ran my code. First, I would write it on MIDE-51 and then compiled it with assembler and created hex file and a list file. I downloaded the hex file to the prototype with Tera Term - through an option of Macro. After I ran the code, the Tera Term would then display the results.