Zilog Z80380 Manual do Utilizador descarregar pdf (Página 72)

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Z380

™

USER'S MANUAL

DC-8297-03

ZILOG

CPI

COMPARE AND INCREMENT (BYTE)

CPI

Operation: A - (HL)

if (XM) then begin

HL(31-0) ← HL(31-0) + 1

end

else begin

HL(15-0) ← HL(15-0) + 1

end

BC(15-0) ← BC(15-0) - 1

This instruction is used for searching strings of byte data. The byte of data at the location

addressed by the HL register is compared with the contents of the accumulator and the Sign

and Zero flags are set to reflect the result of the comparison. The contents of the accumulator

and the memory bytes are unaffected. Two’s complement subtraction is performed. Next the

HL register is incremented by one, thus moving the pointer to the next element in the string.

The BC register, used as a counter, is then decremented by one.

Flags: S: Set if the result is negative; cleared otherwise

Z: Set if the result is zero, indicating that the contents of the accumulator and the memory

byte are equal; cleared otherwise

H: Set if there is a borrow from bit 4 of the result; cleared otherwise

V: Set if the result of decrementing BC is not equal to zero; cleared otherwise

N: Set

C: Unaffected

Addressing Execute

Mode Syntax Instruction Format Time Note

CPI 11101101 10100001 3+r X

1 2 ... 67 68 69 70 71 72 73 74 75 76 77 ... 267 268

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Zilog Z80380 Manual do Utilizador Página 72