A main instruction accepts one or more of the following operands:
| Operand | Description |
| address | A symbolic expression whose effective value is used as an address. |
| $d_reg | Destination register. An integer register that receives a value as a result in an operation. |
| $d_reg/$s_reg | One integer register that is used as both a destination register and a source register. |
| label | A label that identifies a location in a program. |
| offset | An immediate value that is added to the contents of a base register to calculate an effective address. |
| palcode | A value that determines the operation performed by a PAL instruction. |
| $s_reg, $s_reg1, $s_reg2 | Registers whose contents are to be used in an operation. |
| val_expr | An expression whose value is used as an absolute value. |
| val_immed | An immediate value that is to be used in an operation. |
| jhin | An address operand that provides a hint of where a jmp or jsr instruction will transfer control. |
| rhin | An immediate operand that provides software with a hint about how a ret or jsr coroutine instruction is used. |