RST
Call and Return Group
Expansion:
ReStarT
Usage:
rst {00|08|10|18|20|28|30|38}
This maybe regarded as an advanced topic. I haven't been able to find much information or confirm if there are any real uses for this instruction on the ZX Spectrum.
In the 8080 CPU architechure, there was a way to make a more efficient CALL to predefined memory addresses. Unfortunately due to the type of memory the Spectrum has we are unable to modify these predefined memory locations and we can only utilise what is already there.
| Instruction | Description | Opcode |
|---|---|---|
| RST 00 | Jump to memory location 00. Used for various system operations. | C7 |
| RST 08 | Jump to memory location 08. Usually used for error handling and debugging. | CF |
| RST 10 | Jump to memory location 10. Often used for handling keyboard input or other specific operations. | D7 |
| RST 18 | Jump to memory location 18. Typically used for screen output or other I/O operations. | DF |
| RST 20 | Jump to memory location 20. Often used for cassette tape operations. | E7 |
| RST 28 | Jump to memory location 28. Sometimes used for specific print routines, but not recommended directly. | EF |
| RST 30 | Jump to memory location 30. For various other system calls. | F7 |
| RST 38 | Jump to memory location 38. Generally used for handling interrupts. | FF |
Example
rst $28 ; call the routine at this address?