Figure 24. shifting of bcd digits/bytes – Zilog Z08470 User Manual
Page 40
Hardware and Software Implementation
UM008007-0715
28
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
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