ANB6502 Is a Single-Board Computer with VGA Output That Anyone Can Build

Obscure IC enthusiast Anders Nielsen created the ABN6502 SBC. As the name implies, it is a 6502-based single-board computer. This SBC carries the designation R1 since it is an update to a previous design. A significant update to this fully functional computer is how it generates VGA video output.

ANB6502's circuit board measures approximately 75 by 150 millimeters. Along one edge, there are general purpose IO and power header pins. On the other side is an HDB15-connector for VGA output. The DIP-style ICs fill the rest of the PCB.

As the name implies, the core microprocessor is the venerable 6502. This same 8-bit microprocessor was found in many computers in the 1980s. Today it still has a significant following in hobby projects. Another popular chip among 6502 computers is the 6522 "versatile interface adapter (VIA)." Commonly, these chips provide IO such as serial.

Using the capabilities of the 6522, Nielsen breaks out 16 general-purpose IO pins. Another VIA port bit-bangs the more modern interfaces I2C and SPI. Additionally, the I/O chip controls an nRF24L01+.

The nRF24L01+ is a 2.4 GHz RF transceiver that many people use as wireless-UART adapters. The ANB6502 can use this radio to wirelessly bootload the computer.

The display output is one of the significant upgrades over the previous version. The old design used a chip which is challenging to obtain. However, Nielsen cleverly replaced the need for that chip with a 74HC109. This JK-Flip-Flop decodes the sync signaling for the VGA.

That video circuit, the PS/2 adapter, memory map, and a detailed overview are available in this video.

With the update to the VGA circuit, the ABN6502 SBC is a relatively simple build. Anyone with a collection of vintage ICs may even have some of the hardware in their kit already. This GitHub repo contains all of the KiCad design files if you want to order a PCB. For detailed build instructions, check out the ABN6502 project page.