515 Mini 8-bit Processor

515 : Mini 8-bit Processor

Design render

How it works

This project implements a small 8-bit accumulator-based processor. It includes an 8-bit accumulator, program counter, instruction register, address and data registers, a 16-byte memory, input/output register and a five-step fetch/execute sequence. The instruction set provides memory, arithmetic, logic, control-flow, input/output, and accumulator-control operations.

The processor is controlled through rio_in and bidirectional uio_in pins. Results are available on rio_out, while uio_out[7] indicates whether the processor is running.

How to test

Press reset first. To load each memory word, write its address on rio_in, pulse write_ar on uio_in[1], pulse clear_rio on uio_in[0], write the instruction or data value on rio_in, and pulse write_mem on uio_in[3]. The current value of RIO can be observed on rio_out during this process. Repeat this sequence for the following minimal program:

0x00: 0x1A    LOAD 0x0A
0x01: 0x3B    ADD  0x0B
0x02: 0xB1    OUT
0x03: 0x01    HALT
0x0A: 0x05
0x0B: 0x03

For example, to store 0x3B at address 0x01, write 0x01 to rio_in, pulse write_ar, clear RIO, write 0x3B to rio_in, and pulse write_mem. After loading all words, press reset again and pulse start_cpu on uio_in[5] to run the program. The expected result is 0x05 + 0x03 = 0x08, visible on rio_out; run_cpu on uio_out[7] indicates execution and becomes inactive after HALT.

External hardware

List external hardware used in your project (e.g. PMOD, LED display, etc), if any 9 LEDs and 15 push buttons

IO

#InputOutputBidirectional
0rio_in[0]rio_out[0]clear_rio
1rio_in[1]rio_out[1]write_ar
2rio_in[2]rio_out[2]read_ar
3rio_in[3]rio_out[3]write_mem
4rio_in[4]rio_out[4]read_mem
5rio_in[5]rio_out[5]start_cpu
6rio_in[6]rio_out[6]stop_cpu
7rio_in[7]rio_out[7]run_cpu

Chip location

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