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INSTRUCTION SET S3C84E5/C84E9/P84E9
6-34
DA — Decimal Adjust
DA (Continued)
Example: Given: The working register R0 contains the value 15 (BCD), the working register R1 contains 27
(BCD), and the address 27H contains 46 (BCD):
ADD R1,R0 ; C ← "0", H ← "0", Bits 4–7 = 3, bits 0–3 = C, R1 ← 3CH
DA R1 ; R1 ← 3CH + 06
If an 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
the standard binary arithmetic:
0 0 0 1 0 1 0 1 15
+ 0 0 1 0 0 1 1 1 27
0 0 1 1 1 1 0 0 = 3CH
The DA instruction adjusts this result so that the correct BCD representation is obtained:
0 0 1 1 1 1 0 0
+ 0 0 0 0 0 1 1 0
0 1 0 0 0 0 1 0 = 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 the address 27H (@R1).