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;
mov ax, 0x0405 ; unpacked 45 (AH=04, AL=05) add al, 0x03 ; add unpacked 3 → AL=08 aaa ; adjusts if AL>9, increments AH The 6502 has no dedicated BCD arithmetic instructions, but it includes a Decimal Mode flag (D flag in status register). When set, all ADC and SBC instructions automatically perform BCD arithmetic. bcd commands
| Instruction | Description | Operands | |-------------|-------------|----------| | | Decimal Adjust AL after Addition (packed BCD) | implicit (AL) | | DAS | Decimal Adjust AL after Subtraction (packed BCD) | implicit (AL) | | AAA | ASCII Adjust after Addition (unpacked BCD) | implicit (AL, AH) | | AAS | ASCII Adjust after Subtraction (unpacked BCD) | implicit (AL, AH) | | AAM | ASCII Adjust after Multiply (unpacked) | implicit (AX) | | AAD | ASCII Adjust before Division (unpacked) | implicit (AX) | uint8_t bcd_add(uint8_t a, uint8_t b) uint16_t sum =
mov al, 0x45 ; BCD 45 add al, 0x27 ; BCD 27 → binary result 0x6C daa ; adjusts to 0x72 (BCD 72) uint8_t bcd_add(uint8_t a
The 8051 has a DA (Decimal Adjust) instruction that operates on the accumulator after addition.