| Constraint | Used for | Range |
|---|---|---|
| a | Simple upper registers | r16 to r23 |
| b | Base pointer registers pairs | y, z |
| d | Upper register | r16 to r31 |
| e | Pointer register pairs | x, y, z |
| q | Stack pointer register | SPH:SPL |
| r | Any register | r0 to r31 |
| t | Temporary register | r0 |
| w | Special upper register pairs | r24, r26, r28, r30 |
| x | Pointer register pair X | x (r27:r26) |
| y | Pointer register pair Y | y (r29:r28) |
| z | Pointer register pair Z | z (r31:r30) |
| G | Floating point constant | 0.0 |
| I | 6-bit positive integer constant | 0 to 63 |
| J | 6-bit negative integer constant | -63 to 0 |
| K | Integer constant | 2 |
| L | Integer constant | 0 |
| l | Lower registers | r0 to r15 |
| M | 8-bit integer constant | 0 to 255 |
| N | Integer constant | -1 |
| O | Integer constant | 8, 16, 24 |
| P | Integer constant | 1 |
| Q | A memory address based on Y or Z pointer with displacement | |
| R | Integer constant | -6 to 5 |