https://github.com/adumont/hb6502
My Homebrew 6502 breadboard computer with my own #FORTH implementation
https://github.com/adumont/hb6502
6502 6502-assembly breadboard-computer forth
Last synced: 5 days ago
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My Homebrew 6502 breadboard computer with my own #FORTH implementation
- Host: GitHub
- URL: https://github.com/adumont/hb6502
- Owner: adumont
- License: gpl-3.0
- Created: 2021-05-21T18:11:47.000Z (almost 5 years ago)
- Default Branch: main
- Last Pushed: 2024-02-05T22:51:09.000Z (about 2 years ago)
- Last Synced: 2024-04-28T05:53:17.100Z (almost 2 years ago)
- Topics: 6502, 6502-assembly, breadboard-computer, forth
- Language: Assembly
- Homepage:
- Size: 19.7 MB
- Stars: 30
- Watchers: 7
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# Homebrew 6502 SBC
- [Homebrew 6502 SBC](#homebrew-6502-sbc)
- [Introduction](#introduction)
- [Hardware](#hardware)
- [Schematics](#schematics)
- [Memory Map](#memory-map)
- [Software](#software)
- [Monitor](#monitor)
- [AlexFORTH for 6502](#alexforth-for-6502)
- [Datasheets](#datasheets)
- [References](#references)
# Introduction
This project is about building a single board 65c02 computer.
It's powered by a WDC 65C02s CPU driven by a 1.8432MHz oscillator clock, with 32KB of SRAM (only 16K used), 32K of ROM, a 65c22 VIA interface, a 6551 ACIA serial interface, and an 20x4 LCD screen.
The ROM is programmed using my self-made [EEPROM programmer](programmer/README.md).
# Hardware
## Schematics
[Schematics in PDF format](sbc/schematics/easyeda/Schematic_6502.pdf).
## Memory Map
The address decoding logic is following the one described by Garth Wilson in his [6502 Primer, Address decoding](https://wilsonminesco.com/6502primer/addr_decoding.html) page. The corresponding schematics is:
(picture by Garth Wilson from his 6502 Primer)
| Address | Component |
| ------------- | ---------- |
| `$0000-$3FFF` | RAM (16KB) |
| `$4200-$4203` | ACIA |
| `$6000-$600F` | VIA |
| `$8000-$FFFF` | ROM (32KB) |
# Software
## Monitor
At the moment the monitor is very rudimentary, but it serves its purpose.
Monitor will show content at ADDR. You can type:
- a new ADDR (4 char, hex): this will set ADDR to the new value, and display the content. For ex. `04F0`
- a value (2 char, hex): this will store the value at ADDR. For ex. `FB`
- `'` followed by a char: store the char at ADDR. For ex. `'A`
- `j` restore registers to saved values and jump to ADDR
- `c` continue (after a BRK). restore registers to saved values, set ADDR to saved PC (after BRK) and jump to ADDR
Registers manipulation (saved values):
- `aXX` : store XX (hex) in A
- `xXX` : store XX (hex) in X
- `yXX` : store XX (hex) in Y
- `sXX` : store XX (hex) in S
- `pXX` : store XX (hex) in P
- `r` : print registers value
Early demo of the Monitor in Kowalksi 6502 simulator:
## AlexFORTH for 6502
I have implemented my own FORTH kernel for this Homebrew 6502.
Read more here [hb6502/forth](https://github.com/adumont/hb6502/tree/main/forth#alexforth-for-6502).
# Datasheets
- [W65C02S 8–bit Microprocessor](datasheets/w65c02s.pdf)
- [W65C22S Versatile Interface Adapter (VIA)](datasheets/wdc_W65C22S_datasheet_mar_2004.pdf)
- [HD44780U LCD Controller/Driver](datasheets/HD44780.pdf)
- [UM61256FK-15 32K x 8 Bit SRAM](datasheets/UM61256FK-15_SRAM.pdf)
- [AT28C256 32K x8 Paged Parallel EEPROM](datasheets/AT28C256.pdf)
- [HD44780U LCD Controller/Driver](datasheets/HD44780.pdf)
- [SN74HC00 Quadruple 2-Input NAND Gates](datasheets/SN74HC00.pdf)
- [SN74HC138 3-Line To 8-Line Decoders/Demultiplexers](datasheets/SN74HC138.pdf)
- [SN74HC245 Octal Bus Transceivers With 3-State Outputs](datasheets/SN74HC245.pdf)
# References
- [Build a 6502 computer | Ben Eater](https://eater.net/6502)
- [6502 PRIMER: Building your own 6502 computer](https://wilsonminesco.com/6502primer/)
- [Address Decoding](https://wilsonminesco.com/6502primer/addr_decoding.html)
- [ca65 Users Guide](https://cc65.github.io/doc/ca65.html)
- [6502 Instruction Set](https://www.masswerk.at/6502/6502_instruction_set.html)