Hi, I need to design a state machine for a simple CPU. The cpu has a word size of 4 bits, 4 registers, and 2 register ports (A and B) which go to a ‘181 ALU. Our data-input device consists of two DIP switches, which go to the data-in port of the register file. The sole memory employed in this device is featured within the register file. The register file will be comprised of simple ‘273 chips. The selected instructions are addition, transitivity, and subtraction.
Thanks.
To design a state machine for a simple CPU with the given specifications, you need to follow these steps:
1. Identify the states: Start by determining the different states the CPU can be in. In this case, the possible states could be:
- Fetch: Fetching the instruction from memory
- Decode: Decoding the instruction
- Read Registers: Reading the data from the registers
- Perform Operation: Performing the arithmetic operation
- Write Result: Writing the result back to a register
- Halt: Stop the execution
2. Define the inputs: Identify the inputs to the state machine. In this case, the inputs could be:
- Instruction: The current instruction being executed
- Register A and B: The values stored in the registers A and B
- ALU Control: Determines the operation to be performed by the ALU
- DIP Switches: Input data from external sources
- Clock: Synchronizes the state transitions
3. Determine the outputs: Determine the outputs of the state machine. The outputs could include:
- ALU Result: The result produced by the ALU
- Register Write Enable: Signal to enable writing back to a register
- Register Write Address: Address of the register to store the result
4. Map the states: Create a state diagram to map out the transitions between each state based on the inputs and outputs. Assign the necessary control signals for each state transition.
5. Implement the state machine: Based on the state diagram, implement the state machine using hardware elements such as flip-flops, multiplexers, and logic gates. Use appropriate components like '273 chips for the register file and '181 chips for the ALU.
6. Test and verify: Test the state machine design by providing sample inputs and observing the outputs at each state. Verify that the state transitions and outputs are as expected.
It's important to note that the given description only captures a high-level overview of the CPU design. The specific details of the design, such as the instruction encoding, control signals, and timing requirements, need to be further considered and implemented.