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- Custom 4-bit ALU, supporting AND, OR, XOR, NOT, full add and full subtract
- 256 nibbles of general use memory
- Four registers, used for I/O to/from the ALU
- Program counter with jump and jump if zero instructions
| Binary Value | Assembly Mnemonic | A_ARG value | B_ARG value | Operation Description | Implemented |
|---|---|---|---|---|---|
0000 | ADD | None | None | Adds reg 00 to reg 01 and stores in reg 10 | Yes |
0001 | SUB | None | None | Subtracts reg 01 from reg 00 and stores in reg 10 | Yes |
0010 | REG | 4 bit literal | 2 bit register address | StoresA_ARG in regB_ARG | Yes |
0011 | NOP | None | None | None | Yes |
0100 | NOT | None | None | Logically inverts the contents of reg 00 and stores in reg 10 | Yes |
0101 | XOR | None | None | Performs logical XOR on registers 00 and 01 and stores in reg 10 | Yes |
0110 | OR | None | None | Performs logical OR on registers 00 and 01 and stores in reg 10 | Yes |
0111 | AND | None | None | Performs logical AND on registers 00 and 01 and stores in reg 10 | Yes |
1000 | SAV | 8 bit address | 4 bit literal | SavesB_ARG to memory addressB_ARG | Yes |
1001 | LDA | 8 bit address | 2 bit register address | Loads memory addressA_ARG to regB_ARG | Yes |
1010 | WRIT | 8 bit address | 2 bit register address | Saves regB_ARG to memory addressA_ARG | Yes |
1011 | Reserved | - | - | - | No |
1100 | JMP | 6 bit address | None | Jumps to PC addressA_ARG | Yes |
1101 | Reserved | - | - | - | No |
1110 | JCU | 6 bit address | 2 bit register address | If registerB_ARG is equal to register 11, jumps to memory addressA_ARG | Yes |
1111 | Reserved | - | - | - | No |
- There are 4 "namespaces" (bitfields)
Binary range | Use | # uses |
|---|---|---|
0000 -0011 | Arithmetic uses | 2 +NOP |
0100 -0111 | Logical operations | 4 |
1000 -1011 | Memory manipulation operations | 3 |
1100 -1111 | Control flow operations | 3 (only 1 implemented) |
- I think it is Turing-complete or near to it? I am pretty sure it is with manual instruction entry on the ALU/Memory Unit, but the PC I am less sure of
A simple program that adds 1 to a number in memory address 0x00 and stores it in memory address 0x01
LDA0x0000 ; Load the number from memory address 0x00 into reg 00REG101 ; Store the literal 1 in reg 01ADD ; Add reg 00 to reg 01 and store in reg 10WRIT0x0110 ; Write the result to memory address 0x01
Fully designed in Logisim, using the built in TTL library and alsothis library. A few logic gates are included for more obscure ICs, but they will be replaced either with said ICs or with equivalent chips in series.
The ALU/MU is the heart of the computer, and is where all the computation is done. It is a 4-bit ALU, with 256 nibbles of general use memory. The ALU/MU is connected to the program counter, and is where the instructions are executed. The MU contains the registers and the memory.
The program counter is a simple counter that increments by one each clock cycle. It is connected to the ALU/MU, and is where the instructions are fetched from memory. The CLK input loads the current instruction into the ALU/MU, and the GO input executes the instruction. It is programmable, and can jump to any address in memory, using theJMP andJCU instructions.
