Custom-built general purpose, programmable, 6502-based computer and operating system.
- 6502 CPU clocked at 1 Mhz.
- 32KB RAM
- 32KB EEPROM
- Programmable via custom microcontroller based platform.
- 16x2 character LCD display.
- PS/2 keyboard support.
- Built with 7400 series logic contemporary with the original 6502 CPU.
All slide switches must be switched to the right for normal operating mode. Connect a 9V DC power supply and the computer will begin running the program stored in ROM.
To program ROM, slide all switches to the left. Connect a microcontroller dev board (Arduino-like) per wiring guidance in the schematics. Code to perform the programming routine is available in my EEPROM Burner repository.
A small utility, hex.py, has been provided to generate the calls to the write function that are required (in EEPROM Burner) to transfer your binary to the ROM. Create a text file named hex.txt with hex codes, one byte per line, then run:
python hex.py
The included ROM image, 6502.asm, will capture keyboard input and display it on the LCD screen. This serves as a good template from which to build more complex applications.
| Address | Use |
|---|---|
| $0000 | LCD enable |
| $0001 | Unused -- read it to disable any IC (except RAM). |
| $0002 | Current LCD cursor position. |
| $0003 | Flag to indicate if next scan code should be skipped. |
| $0100-$01FF | 6502 stack |
| $7FBE-$7FBF | Temporary location for LCD data manipulation. |
| $7FC0-$7FFF | Data to write to LCD. Each character (16 x 2 lines) is represented by 2 consecutive bytes (4-bit mode). Most sig. 4 bits are for LCD data. Least sig. 4 bits - only bit 3 used (tied to RS pin). |
| $FFF8 | Clock keyboard shift register and enable line buffer. |
| $FFF9 | Reset binary counter (counts bits received from PS/2 keyboard packets). |
| $FFFA | NMI IRQ Vector |
| $FFFB | NMI IRQ Vector |
| $FFFC | Reset Vector - Stores start address of this ROM. |
| $FFFD | Reset Vector |
| $FFFE | IRQ Vector - Keyboard ISR address. |
| $FFFF | IRQ Vector |
| Quantity | Part Type | Properties |
|---|---|---|
| 11 | Ceramic Capacitor | package 200 mil [THT, multilayer]; voltage 6.3V; capacitance 0.1µF |
| 9 | Electrolytic Capacitor | package 100 mil [THT, electrolytic]; voltage 6.3V; capacitance 220µF |
| 1 | Electrolytic Capacitor | package 100 mil [THT, electrolytic]; voltage 6.3V; capacitance 47µF |
| 2 | Electrolytic Capacitor | package 100 mil [THT, electrolytic]; voltage 6.3V; capacitance 22µF |
| 1 | Ceramic Capacitor package | 200 mil [THT, multilayer]; voltage 6.3V; capacitance 0.01µF |
| 3 | 74HC08 Logic AND Gate | variant Variant 1; pins 14; chip label 74HC08; editable pin labels false; package DIP (Dual Inline) [THT]; pin spacing 300mil; part # 74HC08 |
| 3 | 74HCT688E | pins 20; hole size 1.0mm,0.508mm; chip label 74HCT688E; true; package DIP (Dual Inline) [THT]; pin spacing 300mil |
| 1 | 74LS161A | pins 16; hole size 1.0mm,0.508mm; chip label 74LS161A; true; package DIP (Dual Inline) [THT]; pin spacing 300mil |
| 1 | 74LS244AN | pins 20; hole size 1.0mm,0.508mm; chip label 74LS244AN; true; package DIP (Dual Inline) [THT]; pin spacing 300mil |
| 1 | WDC 65C02 | pins 40; hole size 1.0mm,0.508mm; chip label WDC 65C02; true; package DIP (Dual Inline) [THT]; pin spacing 300mil |
| 5 | 74HC04 | pins 14; hole size 1.0mm,0.508mm; chip label 74HC04; true; package DIP (Dual Inline) [THT]; pin spacing 300mil |
| 1 | Voltage Regulator | variant sink; chip 78005; package to220-igo; voltage 5V |
| 1 | 28C256-15 EEPROM | pins 28; hole size 1.0mm,0.508mm; chip label 28C256-15 EEPROM; true; package DIP (Dual Inline) [THT]; pin spacing 300mil |
| 1 | CY7C199-35PC SRAM | pins 28; hole size 1.0mm,0.508mm; chip label CY7C199-35PC SRAM; true; package DIP (Dual Inline) [THT]; pin spacing 300mil |
| 4 | 74LS32 | pins 14; hole size 1.0mm,0.508mm; chip label 74LS32; true; package DIP (Dual Inline) [THT]; pin spacing 300mil |
| 1 | LCD screen | pins 16; type Character |
| 2 | NPN-Transistor | package TO92 [THT]; type NPN (EBC) |
| 2 | 10kΩ Resistor | tolerance ±5%; resistance 10kΩ; package 2512 [SMD] |
| 2 | 5kΩ Resistor | tolerance ±5%; resistance 5kΩ; package 2512 [SMD] |
| 5 | 3.3kΩ Resistor | tolerance ±5%; resistance 3.3kΩ; package 2512 [SMD] |
| 1 | Pushbutton | package [THT] |
| 5 | 74HC595 | package DIP16 [THT]; type 74HC595 |
| 13 | SWITCH_SPDT | package kps-1290 |
| 1 | POT | variant 100k_3362u; package 3362u |
| 1 | mini DIN 6 Connector | variant pth; package mini-din6; connector Mini-DIN6 |
| 1 | Crystal | frequency 1 MHz; package THT; type crystal; pin spacing 5.08mm |