Bcd Commands Updated (PROVEN 2025)

mov ax, dx shr ax, 8 ; high byte of BCD1 mov dx, bx shr dx, 8 ; high byte of BCD2 add al, dl daa mov dl, al mov al, ah adc al, dh daa mov dh, al

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

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. mov ax, dx shr ax, 8 ; high

| 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) | ARM (especially Thumb and Cortex-M) does not have