reset
The reset instruction is the first instruction executed by the system and (partially) initializes the system state.
This instruction is needed because neither the register chips (74HCT670) nor the counters for the address latch (74HCT191) have a master reset.
However, the program counter needs to be 0 before the first instruction can be fetched.
To keep the control logic simple, the easiest way is to encode the reset as an instruction.
To make sure that this instruction is executed first after a reset, we simply make use of the master reset in the instruction latch chips (74HCT173).
This also is why this instruction needs to have opcode 0x00.
| Instruction | Encoding | Semantics | Cycles |
|---|---|---|---|
reset | 00 000 000 | see below | 6 |
The reset instruction performs the following actions:
- disable interrupts