Program 1: Array from Internal Memory
Problem
Suppose that array of 10 data bytes is stored in internal memory location 40h. Write a program in assembly language for 8051 microcontroller to add these data bytes and store the result’s lower byte in 4Ah and MSB in 4Bh.
Algorithm
Step 1: Select Register Bank 0.
Step 2: Initialize Carry Counter.
Step 3: Initialize byte counter.
Step 4: Initialize memory pointer for array.
Step 5: Clear Accumulator which is uses as sum register.
Step 6: Add number from array.
Step 7: If Result < 8 bit, then go to Step 9.
Step 8: Increment Carry counter by 1.
Step 9: Increment memory pointer by 1.
Step 10: Decrement byte counter by 1.
Step 11: If byte counter 1 is not 0, then go to Step 6.
Step 12: Store LSB and MSB (Value of Carry Counter) of result in memory·
Step 13: Stop.
Flowchart
Program
CLR PSW.3 ; Clear 3rd bit of PSW.
CLR PSW.4 ; Clear 4th bit of PSW .
; Above steps are used to select register bank 0.
CLR PSW.7 ; Clear carry flag.
MOV R3, #00H ; Initialize R3=0 as carry counter.
MOV R0, #0AH ; Initialize R0=10(decimal or A hexadecimal) as byte counter.
MOV R1, #40H ; Initialize R1= 40 as memory pointer.
MOV A, #00H ; Clear accumulator.
UP: ADDC A, @R1 ; Add accumulator with data in memory location indicated by R1 indirectly with carry.
JNC NEXT ; if CY=0 then jump to NEXT.
INC R3 ; If carry=1 increment carry counter.
NEXT: INC R1 ; Increment memory pointer.
DJNZ R0, UP ; Decrement and jump to UP if byte counter is not zero
MOV @R1, A ; Store LSB of result to indirect address indicated by R1 indirectly
INC R1 ; Increment memory pointer
MOV A, R3 ; Store MSB of result to accumulator
MOV @R1, A ; Store MSB of result to indirect address indicated by R1 indirectly
LOOP: AJMP LOOP ; Stop.
Program 2: Array from External Memory
Problem
Assume the array of ten data bytes is stored in external RAM from memory location 3000H. Assume sum is 16 bit. Write a program in assembly language for 8051 microcontroller to store LSB of result in memory location 300AH and MSB of result in memory location 300BH.
Algorithm
Step 1: Select Register Bank 0.
Step 2: Initialize Carry Counter.
Step 3: Initialize byte counter.
Step 4: Initialize memory pointer for array.
Step 5: Clear Accumulator which is uses as sum register.
Step 6: Add number from array.
Step7: If Result < 8 bit, then go to Step 9
Step 8: Increment Carry counter by 1
Step 9: Increment memory pointer by 1
Step 10: Decrement byte counter by 1.
Step 11: If byte counter is not 0, then go to Step 6.
Step 12: Store LSB and MSB (Value of Carry Counter) of result in memory.
Step 13: Stop.
Flowchart
Program
CLR PSW.3 ; Clear 3rd bit of PSW.
CLR PSW.4 ; Clear 4th bit of PSW .
; Above steps are used to select register bank 0.
CLR PSW.7 ; Clear carry flag.
MOV R3, #00H ; Initialize R3=0 as carry counter.
MOV R0, #0AH ; Initialize R0=10(decimal or 0A hexadecimal) as byte counter.
MOV DPTR, 3000h ; Initialize memory pointer.
MOV R2, #00H ; Clear R2.
UP: MOVX A, @DPTR ; Move the content of external memory to accumulator.
ADDC A, R2 ; Add accumulator and R2 indirectly with carry.
MOV R2, A ; Store the result to R2
JNC NEXT ; if CY=0 then jump to NEXT.
INC R3 ; If carry=1 increment carry counter.
NEXT: INC DPTR ; Increment memory pointer.
DJNZ R0, UP ; Decrement and jump to UP if byte counter is not zero
MOV @DPTR, A ; Store LSB of result to indirect address indicated by DPTR indirectly
INC DPTR ; Increment memory pointer
MOV A, R1 ; Store MSB of result to accumulator
MOV @DPTR, A ; Store MSB of result to indirect address indicated by DPTR indirectly
LOOP: AJMP LOOP ; Stop.
