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aaa instruction in 8086 with example
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The aaa and daa instructions modify the result of a binary addition to correct it for ASCII or decimal arithmetic. For example, to add two BCD values, you would add them as though they were binary numbers and then execute the daa instruction afterwards to correct the results.
Although this instruction should be used immediately after the addition instruction, it could be used later as long as no other intervening instruction would have changed the AF or CF flags (such as a mov instruction). Example 1: mov al,38h ;packed decimal "38" add al,45h ;add packed decimal "45" daa ;AL = 7Dh -> 83h
Execute DAA only after executing an ADD instruction that leaves a two-BCD-digit byte result in the AL register. The ADD operands should consist of two packed BCD digits. The DAA instruction adjusts AL to contain the correct two-digit packed decimal result.
The DAA instruction is only useful when it follows an ADD instruction that adds (binary addition) two 2-digit, packed BCD values and stores a byte result in the AL Example. ADD AL, BL Before: AL="79H" BL="35H" EFLAGS(OSZAPC)=XXXXXX After: AL="AEH" BL="35H" EFLAGS(0SZAPC)=110000. DAA Before: AL="AEH"
3 Jun 2014 The DAA instruction (Decimal Adjust Accumulator) allows conversion of the 8-bit accumulator value to Binary Coded Decimal (BCD). Example 1: mov al,38h ;packed decimal "38" add al,45h ;add packed decimal "45" daa ;AL = 7Dh -> 83h (with CF clear = 83 packed decimal) AL CF AF ; after addition 7Dh
The DAA (Decimal Adjust after Addition) instruction allows addition of numbers represented in 8-bit packed BCD code. It is used immediately after normal addition instruction operating on BCD codes. This instruction assumes the AL register as the source and the destination, and hence it requires no operand.
I must say, I've never seen a dafter instruction spec. If you examine the table carefully, you will see that the effect of the instruction depends only on the C and H flags and the value in the accumulator -- it doesn't depend on the previous instruction at all. Also, it doesn't divulge what happens if, for example,
12 Apr 2017
Adjusts the sum of two packed BCD values to create a packed BCD result. The AL register is the implied source and destination operand. The DAA instruction is only useful when it follows an ADD instruction that adds (binary addition) two 2-digit, packed BCD values and stores a byte result in the AL register.
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