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INSTRUCTION SET
S3C831B/P831B
DA — Decimal Adjust
DA
(Continued)
Example:
Given: Working register R0 contains the value 15 (BCD), working register R1 contains
27 (BCD), and address 27H contains 46 (BCD):
ADD
DA
R1,R0
R1
C ← "0", H ← "0", Bits 4–7 = 3, bits 0–3 = C, R1 ← 3CH
R1 ← 3CH + 06
;
;
If addition is performed using the BCD values 15 and 27, the result should be 42. The sum is
incorrect, however, when the binary representations are added in the destination location using
standard binary arithmetic:
0001
+ 0010
0101
0111
0011
1100
15
27
=
3CH
The DA instruction adjusts this result so that the correct BCD representation is obtained:
0011
+ 0000
1100
0110
0100
0010
=
42
Assuming the same values given above, the statements
SUB
27H,R0 ;
C ← "0", H ← "0", Bits 4–7 = 3, bits 0–3 = 1
DA
@R1
@R1 ← 31–0
;
leave the value 31 (BCD) in address 27H (@R1).
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