Zilog Z08470 Manual do Utilizador descarregar pdf (Página 40)

100

101

Hardware and Software Implementation UM008007-0715

Z80 CPU

User Manual

LD HL, DATA ;ADDRESS OF FIRST BYTE

LD B, COUNT ;SHIFT COUNT

XOR A ;CLEAR ACCUMULATOR

ROTAT: RLD ;ROTATE LEFT low-order DIGIT IN ACC

;WITH DIGITS IN (HL)

INC HL ;ADVANCE MEMORY POINTER.

DJNZ ROTAT-$ ;DECREMENT B AND GO TO ROTAT IF

;B IS NOT ZERO, OTHERWISE FALL

;THROUGH

Eleven bytes are required for this operation.

Example 4

One number is to be subtracted from another number, both of which exist in packed BCD

format and are of equal but varying length. The result is stored in the location of the minu-

end. The operation is programmed as follows:

LD HL, ARG1 ;ADDRESS OF MINUEND

LD DE, ARG2 ;ADDRESS OF SUBTRAHEND

LD B, LENGTH ;LENGTH OF TWO ARGUMENTS

AND A ;CLEAR CARRY FLAG

SUBDEC:LD A, (DE) ;SUBTRAHEND TO ACC

Figure 24. Shifting of BCD Digits/Bytes

1 2 ... 35 36 37 38 39 40 41 42 43 44 45 ... 325 326

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Zilog Z08470 Manual do Utilizador Página 40

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