193 8-bit Accumulator CPU SoC
193 : 8-bit Accumulator CPU SoC
- Author: Fidel Makatia
- Description: 8-bit accumulator microcontroller with 33-instruction ISA, 32-word ROM, 32-byte RAM, hardware stack, UART TX, and timer/counter
- GitHub repository
- Open in 3D viewer
- Clock: 5000000 Hz
How it works
This is a complete 8-bit accumulator-based microcontroller SoC with:
- 33-instruction ISA: arithmetic (ADD, SUB, INC, DEC), logic (AND, OR, XOR, NOT), shifts (SHL, SHR), memory (LDA, STA, LDM, ADDA, SUBA), branching (JMP, JZ, JNZ, JC), stack (PUSH, POP, CALL, RET), I/O (IN, OUT), UART (UTXD, UTXS, UBRD), timer (TSET, TGET, TCLR), and control (NOP, HLT)
- 3/4-stage FSM pipeline: FETCH, DECODE, [MEM_READ], EXECUTE. The MEM_READ stage is used for memory-to-ALU instructions (ADDA/SUBA) and stack reads (POP/RET)
- 32-word x 16-bit program ROM with a hardcoded demo program
- 32-byte x 8-bit data RAM (shared with hardware stack)
- Hardware stack: 5-bit stack pointer, grows downward from 0x1F, supports PUSH/POP/CALL/RET for subroutines
- UART transmitter: 8-N-1 serial output with programmable baud rate divisor
- Timer/counter: 8-bit free-running counter with programmable 8-bit prescaler
- 8-bit GPIO with latched output and pass-through input
The demo program counts 1 to 5 on GPIO, calls a subroutine (demonstrating CALL/RET), sends 'H' over UART, reads the timer, outputs 42, then halts.
How to test
- Apply reset: hold
rst_nlow for at least 5 clock cycles - Release reset and assert
ena(both high) - Observe
uo_outpins counting: 1, 2, 3, 4, 5 - After counting, the program demonstrates CALL/RET (GPIO shows 6), UART TX, timer (GPIO shows timer count), and final value (GPIO shows 42)
uio_out[0]goes high when the CPU haltsuio_out[1]carries the UART TX serial output- Optionally connect switches to
ui_infor GPIO input (used by the IN instruction)
External hardware
- Connect 8 LEDs to
uo_out[7:0]to visualize GPIO output - Connect 1 LED to
uio_out[0]to indicate CPU halt status - Connect a USB-UART adapter RX to
uio_out[1]for serial output (configure baud rate via UBRD instruction) - Optionally connect a DIP switch or buttons to
ui_in[7:0]for GPIO input
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | gpio_in[0] | gpio_out[0] | halted (output) |
| 1 | gpio_in[1] | gpio_out[1] | uart_tx (output) |
| 2 | gpio_in[2] | gpio_out[2] | |
| 3 | gpio_in[3] | gpio_out[3] | |
| 4 | gpio_in[4] | gpio_out[4] | |
| 5 | gpio_in[5] | gpio_out[5] | |
| 6 | gpio_in[6] | gpio_out[6] | |
| 7 | gpio_in[7] | gpio_out[7] |