Programming Microcontroller AT89C51

 Microcontroller has a function as microprocessor. The different is simplicity of microcontroller that can stand alone with out any component such ADC and external memory. Microcontroller is a kind of integrated circuit that be packed as common IC. The main different is the ability to run the instruction code that is loaded at it's memory. On the other hand, microcontroller is completed with Arithmetic Logic Unit that can run arithmetic operations. With out a program that was loaded in it's memory, microcontroller can do nothing.

Microcontroller AT89C51

Microcontroller AT89C51 is a product of Atmel Corp, that belong to MCS51 microcontroller family. This microcontroller has a same architecture with  microcontroller 8031, product of Intel Corp. The specification of microcontroller AT89C51 are stated below:

- 8 bit data line

- 4K Byte of flash memory

- Maximum clock frequency is 24MHz

- 128 Byte internal  Memory  

- Four I/O port

- Dual  16 bit timer/counter

Registers of AT89C51

Microcontroller AT89C51 has some registers, registers that explain in this tutorial are:

- Accumulator

- R0 - R7

Example of Simple Program

Here are two simple listing program in assembly language, The used assembler is asm51.exe

Figure 1. At89c51 Application Circuit for running led and seven segment display.

- Running Led

Figure 2. A photograph of Running Led Circuit.

$mod51

      org 00h

      jmp mulai

;program dimulai di sini

mulai:

      mov r1, #05h

loop: 

      dec r1

      mov a, #01h

      mov p1, a

      call tunda

kiri:

rl a

      mov p1, a

      call tunda

      cjne a, #80h, kiri

kanan:

      rr a

      mov p1, a

      call tunda

      cjne a, #01h, kanan

      cjne r1, #00h, loop

      ljmp mulai

;

tunda:

      mov r4, #02h

ulang:

      dec r4

      mov r3, #0ffh

tunda1:

      dec r3

      mov r2, #0ffh

tunda2:      

dec r2

      cjne r2, #00h, tunda2

      cjne r3, #00h, tunda1

      cjne r4, #00h, ulang

      ret

end

The registers that are used above are r1 to r4, and accumulator too. The port that is used to light on eight LEDs is P1.

- Displaying a Number Using Seven Segment Display

Figure 3. A Photograph of Seven Segment Displaying Circuit.

$mod51

      org 00h

      jmp mulai

mulai:         

mov r6, #00h

      mov a, #00h

ulang:         

      mov r6, p2

      mov p1, r6

      lcall tampil1

      mov p2, #01000000b

      lcall tunda

      lcall tampil2

      mov p2, #10000000b

      lcall tunda

      jmp ulang

tampil1:mov a, #00h

      clr c

      mov b, #10

      mov a, r6

      div ab

      cjne a, #00h, ke_1

      ljmp nol1

ke_1:          cjne a, #01h, ke_2

      ljmp siji

ke_2:          cjne a, #02h, ke_3

      ljmp loro 

ke_3:          cjne a, #03h, ke_4

      ljmp telu 

ke_4:          cjne a, #04h, ke_5

      ljmp papat

ke_5:          cjne a, #05h, ke_6

      ljmp lima

ke_6:          cjne a, #06h, ke_7

      ljmp enem

ke_7:          cjne a, #07h, ke_8

      ljmp pitu

ke_8:          cjne a, #08h, ke_9

      ljmp wolu

ke_9:          cjne a, #09h, keluar

      ljmp sanga

keluar: ret

tampil2:mov a, #00h

      clr c

      mov a, b

      cjne a, #00h, ke_12

      ljmp nol

ke_12: cjne a, #01h, ke_22

      ljmp siji

ke_22:        cjne a, #02h, ke_32

      ljmp loro 

ke_32:        cjne a, #03h, ke_42

      acall telu 

ke_42:        cjne a, #04h, ke_52

      ljmp papat

ke_52:        cjne a, #05h, ke_62

      ljmp lima

ke_62:        cjne a, #06h, ke_72

      ljmp enem

ke_72:        cjne a, #07h, ke_82

      ljmp pitu

ke_82:        cjne a, #08h, ke_92

      ljmp wolu

ke_92:        cjne a, #09h, keluar2

      ljmp sanga

keluar2:ret

                       ;      a

                       ;    f      b

                       ;      g 

                       ;    e      c

                       ;      d                    

                       ;0gfedcba

nol1:           mov p0, #00h

      ret

nol: mov p0, #00111111b

      ret

siji: mov p0, #00000110b

      ret

loro:           mov p0, #01011011b

      ret

telu:            mov p0, #01001111b

      ret

papat:         mov p0, #01100110b

      ret

lima:           mov p0, #01101101b

      ret

enem:         mov p0, #01111101b

      ret

pitu:            mov p0, #00000111b

      ret

wolu:          mov p0, #01111111b

      ret

sanga:         mov p0, #01101111b

      ret

tunda:  mov r5, #255

kurang: dec r5

      cjne r5, #00h, kurang

      ret

end

The listing program above, has a function to display two binary datum that saved in r6. The used display are two seven segment common cathode LED. Datum at a segment to g are attached from P0.0 -P0.6. For sweeping digit once and second we use P2.7 and p2.8