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Arithmetic Group Instructions (Part-III)

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SUB R:
  • This instruction subtract the contents of specified register from the contents of the accumulator.
  • Register R can by any general purpose register like A, B, C, D, E, H and L.
  • The result is stored in accumulator.
  • Subtraction is performed by 2's complement method.
  • All flags are affected.
  • It is a one byte instruction.
  • Register addressing mode is used.
Example:
If A =50H and C = 30H
SUB C ; This instruction subtracts the contents of C (30H) from the contents of A (50H) and the result (20H) is stored in A.

SUB M:
  • This instruction subtract the contents of the memory location pointed by HL register pair from the contents of the accumulator.
  • The result is stored in accumulator.
  • Subtraction is performed by 2's complement method.
  • All flags are affected.
  • It is a one byte instruction.
  • Register indirect addressing mode is used.
Example:
If HL = 1000H, (1000H) = 10H and A = 40H
SUB M ; This instruction subtracts the contents of location 1000H i.e. 10H from the contents of A (40H) and result 30H is stored in A.

SBB R:
  • This instruction subtract the contents of specified register and carry flag (borrow flag for subtraction) from the contents of the accumulator.
  • Register R can by any general purpose register like A, B, C, D, E, H and L.
  • The result is stored in accumulator.
  • All flags are affected.
  • It is a one byte instruction.
  • Register addressing mode is used.
Example:
If CY = 1, A = 40H and C = 20H
SBB C ; This instruction subtracts the contents of C (20H) and carry (1) from the contents of A (40H) and the result (1FH) is stored in A.

SBB M:
  • This instruction subtract the contents of the memory location pointed by HL register pair and borrow flag from the contents of the accumulator.
  • The result is stored in accumulator.
  • All flags are affected.
  • It is a one byte instruction.
  • Register indirect addressing mode is used.
Example:
If CY = 1, HL =1000H, (1000H) = 10H and A = 50H
SBB M ; This instruction subtracts the contents of location 1000H i.e. 10H and carry (1) from the contents of A (50H) and result 3FH is stored in A.
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