Daa Instruction In 8085 Microprocessor Apr 2026

The DAA (Decimal Adjust Accumulator) instruction is a specialized arithmetic command in the 8085 microprocessor designed to facilitate Binary Coded Decimal (BCD) arithmetic. While the 8085's Arithmetic Logic Unit (ALU) natively performs binary addition, most human-facing systems—like calculators or digital clocks—require results in base-10. The DAA instruction bridges this gap by automatically correcting binary results into valid packed BCD format, where each 8-bit byte represents two decimal digits (00 to 99).

One of the most important constraints of the DAA instruction is that it must be executed immediately following an ADD, ADC, or INR operation. It does not work correctly after subtraction (SUB or SUI) because the 8085 lacks a "Decimal Adjust for Subtraction" equivalent, which is found in later processors like the Z80. Furthermore, DAA is an "implied" addressing mode instruction, meaning it requires no operands; it always acts exclusively on the contents of the Accumulator register. Daa Instruction In 8085 Microprocessor

Operationally, DAA follows a two-step logic based on the status of the processor's flags and the values of the two 4-bit nibbles in the accumulator. First, it examines the lower nibble (bits D0-D3). If this value is greater than 9, or if the Auxiliary Carry (AC) flag is set to 1, the instruction adds 6 (06H) to the accumulator. Second, it examines the upper nibble (bits D4-D7). If this value is now greater than 9, or if the Carry (CY) flag is set to 1, the instruction adds 96 (60H) to the accumulator. These additions of 6 or 60 force a carry-over into the next higher digit, effectively converting base-16 overflows into base-10 carries. The DAA (Decimal Adjust Accumulator) instruction is a