ld a, $45 add a, $27 daa ; A becomes $72 The Z80 DAA uses carry and half-carry flags to correct the accumulator. ARM (especially Thumb and Cortex-M) does not have dedicated BCD arithmetic instructions. BCD operations must be implemented via software routines, using bit manipulation and conditional addition/subtraction.
| Command | Effect in Decimal Mode | |---------|------------------------| | | Set Decimal Mode (D=1) | | CLD | Clear Decimal Mode (D=0, back to binary) | | ADC | Adds with carry in BCD | | SBC | Subtracts with borrow in BCD | bcd commands
uint8_t bcd_add(uint8_t a, uint8_t b) uint16_t sum = (a & 0x0F) + (b & 0x0F) + (((a >> 4) + (b >> 4)) << 4); if ((sum & 0x0F) >= 10) sum += 6; if ((sum >> 4) >= 10) sum += 0x60; return (uint8_t)sum; ld a, $45 add a, $27 daa ;
The 8051 has a DA (Decimal Adjust) instruction that operates on the accumulator after addition. | Command | Effect in Decimal Mode |