# `adda`

[M68K Documentation](https://asm-editor.specy.app/documentation/m68k.md) › [Instructions](https://asm-editor.specy.app/documentation/m68k/instruction.md)

Web page: https://asm-editor.specy.app/documentation/m68k/instruction/adda

**Add address**

Category: Arithmetic

Adds the first operand to an address register, sign extending a word to long and leaving sr unchanged.

Sizes .w .l, .w by default

## Flags

| Flag | Effect |
| --- | --- |
| X | not changed |
| N | not changed |
| Z | not changed |
| V | not changed |
| C | not changed |

## Forms

- `adda <ea>, An`
  - Source: Dn, An, (An), (An)+, -(An), d(An), d(An,Xn), abs, d(PC), d(PC,Xn), #imm (all modes)

## Operands

- [`<ea>`](https://asm-editor.specy.app/documentation/m68k/addressing-mode.md): An operand using one of the addressing modes listed for this form. The list determines whether it can be a register, memory or an immediate value. With `opt p=68020`, an allowed `d(An,Xn)` or `d(PC,Xn)` mode also permits the corresponding 68020 indexed and memory indirect forms. See [68020 addressing](https://asm-editor.specy.app/documentation/m68k/addressing-mode/68020.md).
- [`An`](https://asm-editor.specy.app/documentation/m68k/addressing-mode/direct.md): An address register, `a0` to `a7`; `sp` is another name for `a7`.
- [`#imm`](https://asm-editor.specy.app/documentation/m68k/addressing-mode/immediate.md): An immediate value written after `#`: a number, character or label, such as `#10`, `#$FF` or `#'a'`. It must fit the operation’s size: byte `-128` to `255`, word `-32768` to `65535`, or long `-2147483648` to `4294967295`; signed and unsigned spellings are accepted.

## Description

It does not change the SR.  When using word size, the first operand is sign extended to long and the second is read and written as a long.

## Example

```m68k
* --- Word is sign-extended before adding ---
move.l #$10000, a0
adda.w #$FFFE, a0 ; $FFFE sign-extends to $FFFFFFFE (-2)

* --- Long adds as-is ---
move.l #$10000, a1
adda.l #$10000, a1

* --- Does NOT affect flags (compare with add) ---
move.l #$10000000, d0
move.l #$10000000, a2
add.l #$F0000000, d0 ; wraps to zero and sets carry
adda.l #$F0000000, a2 ; flags unchanged
```