# Stack based 8-Bit processor

## Peripherals

Connected to a bidirectional bus.

## Instruction set

| Operand Code | Instruction | Signature | Description                                            |
| ------------ | ----------- | --------- | ------------------------------------------------------ |
| 00000000     | nop         |           | Just do nothing for a cycle straight                   |
| 00010000     | int         | interrupt | Interrupt code to call on PIA                          |
| 00100000     | jmp         | label     | Jump to label if last operation had non zero result    |
| 00110000     | wfi         | interrupt | Wait for interrupt. If interrupt is zero, wait for any |
| 00000100     | push        | stack, rx | Push the rx value to the index stack                   |
| 00010100     | pop         | stack, rx | Pop into the register rx from index stack              |
| 00001000     | read        | rdx       | Read from PIA into the target register                 |
| 00011000     | write       | rdx       | Write to PIA the value of target register              |
| 00000010     | not         | rx        | negates rx                                             |
| 00010010     | par         | rx        | parity of rx                                           |
| 00100010     | cnt         | rx        | count of set bits in rx                                |
| 00110110     | and         | rx,r1     | Store and of rx and r1 into rx                         |
| 01000110     | or          | rx,r1     | Store or of rx and r1 into rx                          |
| 01010110     | xor         | rx,r1     | Store xor of rx and r1 into rx                         |
| 01100110     | mov         | rx,r1     | overwrite rx with r1                                   |
| 01110110     | sl          | rx,r1     | shift rx left by r1                                    |
| 10000110     | sr          | rx,r1     | shift rx right by r1                                   |
| 00001010     | add         | rx,r1     | Add r1 to rx                                           |
| 00011010     | sub         | rx,r1     | Subtract r1 from rx                                    |
| 00001110     | seq         | rx,ry     | Set if rx = ry                                         |
| 00011110     | slt         | rx,ry     | Set if rx < ry                                         |
| 00101110     | sltu        | rx,ry     | set if abs(rx) < abs(ry)                               |

### Instruction Types

| From     | To       | Type               |
| -------- | -------- | ------------------ |
| 00000000 | 11111110 | Base Instructions  |
| 00000001 | 11111111 | Possible extension |