In this article two Assembly language programs for 8051 microcontroller are explained to find 2’s complement of an 8 bit Number.
8051 Program to find 2’s complement of an 8 bit Number
To find 2's complement of a number stored in register bank
Problem 1
Write an assembly language program to find 2’s complement of a number stored in Register R0 of Register Bank 0 and store the result in R1 of same bank of for 8051 microcontroller.
Algorithm
Finding 2’s Complement of a Number
- Select the register bank using PSW register.
- Load the number from Register R0.
- Invert all the bits of the number to get the 1’s complement.
- Add 1 to the 1’s complement to obtain the 2’s complement.
- Store the result in Register R1.
- Stop
Program
CLR PSW.4 ; Clear bit 4 of PSW register.
CLR PSW.3 ; Select register bank 0.
MOV A, R0 ; Load the number from R0 to Accumulator A.
CPL A ; Complement all bits to get 1’s complement.
INC A ; Increment the 1’s complement to get 2’s complement.
MOV R1, A ; Store the 2’s complement in R1.
Loop: AJMP Loop ; End of program.
Note:
Apart from using INC A instruction you can use ADD A,#01H instruction, which will increase the contents of accumulator by 1.
Tutorial on 8051 Program to Find 2’s complement
To find 2's complement of a number stored in external memory
Problem 2
Write an assembly language program to find 2’s complement of a number stored in memory location 3000H of external memory of 8051 microcontroller and store the result in 3001H.
Algorithm
Finding 2’s Complement of a Number
- Initialize the memory pointer.
- Load the number from memory location 3000H.
- Invert all the bits of the number to get the 1’s complement.
- Add 1 to the 1’s complement to obtain the 2’s complement.
- Store the result in memory location 3001H.
- End the program.
Program
MOV DPTR, #3000H ; Load address of memory location 3000H to DPTR.
MOVC A, @DPTR ; Move data from memory to Accumulator A.
CPL A ; Complement all bits to get 1’s complement.
INC A ; Increment the 1’s complement to get 2’s complement.
INC DPTR ; Load address of memory location 3001H to DPTR.
MOV @DPTR, A ; Store the 2’s complement in memory location 3001H.
Loop: AJMP Loop ; End of program.
