Description
This is an attempt to build a CPU from scratch; first in Logisim and then with ICs. CPU.circ is the version before implementing the memory device bus, CPU_2.circ is the newer version which also implements pointer manipulation as well as conditional skip for branching.
Instructions
Instructions consist of an 8 bit argument followed by the 8 bit command. The usage of the argument depends on the context. For example, the instruction to load the value 0x34 into the accumulator is 0x3481.
List of instructions (HEX)
| Base | HEX | Assembly | Short name | Additional information | Usage example | Ticks |
|---|---|---|---|---|---|---|
| 0x08 | 0x08 | cload0 | Cache 0 load | From memory address | cload0 r0 | 4 |
| 0x09 | cload1 | Cache 1 load | cload1 r0 | 4 | ||
| 0x88 | icload0 | Cache 0 load | Immediate | icload0 d0 | 3 | |
| 0x89 | icload1 | Cache 1 load | icload1 d0 | 3 | ||
| 0x10 | 0x10 | add | Add to memory | Cache 0 + Cache 1 | add r0 | 4 |
| 0x11 | sub | Sub to memory | sub r0 | 4 | ||
| 0x12 | mul | Mul to memory | mul r0 | 4 | ||
| 0x13 | div | Div to memory | div r0 | 4 | ||
| 0x14 | and | Bitwise And to memory | Cache 0 AND Cache 1 | and r0 | 4 | |
| 0x15 | or | Bitwise Or to memory | or r0 | 4 | ||
| 0x16 | xor | Bitwise Xor to memory | xor r0 | 4 | ||
| 0x17 | inv | Invert cache 0 to memory | NOT cache 0 | inv r0 | 4 | |
| 0x90 | addc | Add to cache 0 | Replaces existing data in cache 0 | addc | 3 | |
| 0x91 | subc | Sub to cache 0 | subc | 3 | ||
| 0x92 | mulc | Mul to cache 0 | mulc | 3 | ||
| 0x93 | divc | Div to cache 0 | divc | 3 | ||
| 0x94 | andc | Bitwise And to cache 0 | andc | 3 | ||
| 0x95 | orc | Bitwise Or to cache 0 | orc | 3 | ||
| 0x96 | xorc | Bitwise Xor to cache 0 | xorc | 3 | ||
| 0x97 | invc | Invert cache 0 to cache 0 | invc | 3 | ||
| 0x18 | 0x18 | mov | Copy data | Register to register | mov r0, r1 | 7 |
| 0x98 | imov | Copy data | Immediate | imov d0, r0 | 6 | |
| 0x20 | 0x20 | false | Skip if (false) | Never skips | 2 | |
| 0x21 | gr | Skip if (cache 0 > cache 1) | Signed. Skips two instructions | gr | 3/2 | |
| 0x22 | eq | Skip if (cache 0 == cache 1) | eq | 3/2 | ||
| 0x23 | ge | Skip if (cache 0 >= cache 1) | ge | 3/2 | ||
| 0x24 | le | Skip if (cache 0 < cache 1) | le | 3/2 | ||
| 0x25 | ne | Skip if (cache 0 != cache 1) | ne | 3/2 | ||
| 0x26 | leq | Skip if (cache 0 <= cache 1) | leq | 3/2 | ||
| 0x27 | true | Skip if (true) | Always skips | 3 | ||
| 0xa0 | false | 2 | ||||
| 0xa1 | ugr | Unsigned | ugr | 3/2 | ||
| 0xa2 | ueq | ueq | 3/2 | |||
| 0xa3 | uge | uge | 3/2 | |||
| 0xa4 | ule | ule | 3/2 | |||
| 0xa5 | une | une | 3/2 | |||
| 0xa6 | uleq | uleq | 3/2 | |||
| 0xa7 | true | 3 | ||||
| 0x28 | 0x28 | jmp | Jump | Address saved in register | jmp r0 | 4 |
| 0xa8 | ijmp | Immediate | ijmp d0 | 4 | ||
| 0x00 | 0x00 | drp | Do nothing | Does nothing | 2 |