Skip to main content

Arithmetic Group Instructions (Part-IV)

By
SUI 8-bit data:
  • This instruction subtracts the 8-bit data given in the instruction from the contents of the accumulator.
  • The result is stored in accumulator.
  • All flags are modified.
  • It is a two byte instruction.
  • Immediate addressing mode is used.
Example:
If A = 50H
SUI 10H ; This instruction subtracts 10H from the contents of A (50H) and the result (40H) is stored in A.

SBI 8-bit data:
  • This instruction subtracts the 8-bit data given in the instruction and the borrow flag from the contents of the accumulator.
  • The result is stored in accumulator.
  • All flags are modified.
  • It is a two byte instruction.
  • Immediate addressing mode is used.
Example:
If CY = 1 and A = 50H
SBI 20H ; This instruction subtracts 20H and carry (1) from the contents of A (50H) and the result (2FH) is stored in A.

DAA:
  • It stands for Decimal Adjust Accumulator.
  • This instruction adjusts accumulator to packed BCD after adding two BCD numbers.
  • If the value of low order four bits D3-D0 in accumulator is greater than 9 or if AC (Auxiliary Carry) flag is set, then instruction adds 6 to the low order four bits.
  • If the value of high order four bits D7-D4 in accumulator is greater than 9 or if CY (Carry) flag is set, then instruction adds 6 to the high order four bits.
  • This is the only instruction that uses AC (Auxiliary Carry) flag.
  • All flags are modified.
  • It is a one byte instruction.
  • Implied addressing mode is used.
Example:
If A = 0101 1001 = 59 BCD
and B = 0001 0011 = 13 BCD then
ADD B            ; This adds A and B and gives A = 0110 1100 = 6CH
DAA                ; This instruction adds 0000 0110 = 06H to 6CH because 1100 > 9
                         ; So A = 0111 0010 = 72 BCD

If A = 1001 0101 = 95 BCD
and B = 0001 0011 = 13 BCD
ADD B             ; This adds A and B and gives A = 1010 1000 = A8H
DAA                 ; This adds 0110 0000 = 60H to A8H because 1010 > 9
                         ; So A = 0000 1000 = 08 BCD and CY = 1
Labels:

Comments

Post a Comment

Popular posts from this blog

Program to pack the two unpacked BCD numbers

By
Statement: Pack the two unpacked BCD numbers stored in memory locations 2000H and 2001H and store the result in memory location 2002H. The least significant digit is stored at 2000H. Example: (2000H) = 04H (2001H) = 09H Result = (2002H) = 94H Program: LDA 2001H                        ; Obtain the most significant BCD digit RLC                                    ; Rotate left  RLC                                    ; Rotate left  RLC                                    ; Rotate left  RLC                                    ; Rotate left...
Post a Comment
Read more

Program to exchange the contents of two memory locations

By
Statement: Exchange the contents of memory locations 2000H and 2001H. Example:  Initially, (2000H) = 34H (2001H) = 20H After exchanging, (2000H) = 20H (2001H) = 34H Program 1 using direct addressing instructions: LDA 2000H               ; Get the contents of location 2000H into accumulator MOV B, A                  ; Move the contents of accumulator into register B LDA 2001H                ; Get the contents of location 2001H into accumulator STA 2000H                 ; Store the contents of accumulator into location 2000H MOV A, B                  ; Move the contents of register B into accumulator STA 2001H                 ; Store the contents of accumulator into location 2001H HLT  ...
Post a Comment
Read more

Stack Operations Instructions (Part-II) - SPHL and XTHL

By
SPHL: This instruction copies the contents of HL register pair to the stack pointer (SP). It means that the stack pointer will now point to the memory location whose address was given in the HL register pair. No flags are affected. It is a one byte instruction. Register addressing mode is used. Example: If HL = 2030H, then SPHL ; This instruction will copy 2030H into SP. So SP will point to the memory location 2030H. XTHL: This instruction exchanges the contents of the memory location pointed by stack pointer with the contents of the L register and the contents of the next memory location with the contents of H register. This instruction does not alter the contents of the stack pointer. No flags are affected. It is a one byte instruction. Register Indirect addressing mode is used. Example: If HL = 5601H, SP = 2000H, (2000H) = 30H and (2001H) = 20H, then XTHL ; This instruction will exchange the contents of the memory location 2000H i.e. 3...
Post a Comment
Read more