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 necessity of DAA arises from the fact that binary addition of BCD numbers often yields "illegal" results. For example, adding decimal 9 (1001) and decimal 1 (0001) in binary results in 1010 (hexadecimal A). In BCD, however, the result should be 10, represented as 0001 0000. The DAA instruction detects these discrepancies and applies a correction factor to ensure the final value in the accumulator matches decimal logic. Daa Instruction In 8085 Microprocessor

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). Operationally, DAA follows a two-step logic based on

An example showing how to add two large decimal numbers. Second, it examines the upper nibble (bits D4-D7)