Addition of Two 8 Bit Numbers in 8051 Microcontroller Using Ports
8051 microcontroller is a microcontroller designed by Intel in 1981. It is an 8-bit microcontroller with 40 pins DIP (dual inline package), 4kb of ROM storage and 128 bytes of RAM storage, 2 16-bit timers. It consists of four parallel 8-bit ports, which are programmable as well as addressable as per the requirement.
Problem: To write an assembly language program to add two 8 bit numbers in 8051 microcontroller using ports.
- Initialize Ports P0 and P1 as input ports.
- Initialize Ports P2 and P3 as output ports.
- Initialize the R1 register.
- Move the contents from Port 0 to B register.
- Move the contents from Port 1 to A register.
- Add contents in A and B.
- If carry is present increment R1.
- Move contents in R1 to Port 2.
- Move the sum in step 6 to Port 3.
ORG 00H // Indicates starting address MOV P0,#0FFH // Initializes P0 as input port MOV P1,#0FFH // Initializes P1 as input port MOV P2,#00H // Initializes P2 as output port MOV P3,#00H // Initializes P3 as output port L1:MOV R1, #00H // Initializes Register R1 MOV B,P0 // Moves content of P0 to B MOV A,P1 // Moves content of P1 to A CLR C // Clears carry flag ADD A,B // Add the content of A and B and store result in A JNC L2 // If carry is not set, jump to label L2 INC R1 // Increment Register R1 if carry present L2: MOV P2, R1 // Moves the content from Register R1 to Port2 MOV P3,A // Moves the content from A to Port3 SJMP L1 // Jumps to label L1 END
- ORG 00H is the starting address of the program.
- Giving the values as #0FFH and #00H initializes the ports as input and output ports respectively.
- R1 register is initialized to 0 so as to store any carry produced during the sum.
- MOV B, P0 moves the value present in P0 to the B register.
- MOV A, P1 moves the value present in P1 to Accumulator.
- ADD AB adds the values present in Accumulator and B register and stores the result in Accumulator.
- JNC L2 refers to jump to label L2 if no carry is present by automatically checking whether the carry bit is set or not.
- If the carry bit is set to increment register R1.
- MOV P2, R1, and MOV P3, A refers to moving the carry bit to P2 and result in Accumulator to P3.