NOTE: I’m going to experiment with turning on commenting, starting with this post. We’ll see how it goes.
The nice thing about creating things as a hobby is that you can switch to a new thing whenever you get bored or frustrated with the current thing. That is exactly what happened to me a few months ago: I started getting frustrated with the limited features I had available on COLE-1, so I decided to just jump ahead and start the next iteration. The result is this:
That ugly mess of wires is actually a functional 2 MHz 65816-based SBC, called, not surprisingly, COLE-2.
Hardware Overview
COLE-2 will be a substantial upgrade from its predecessor:
- 6 MHz 65C816 CPU (largely limited by EEPROM speeds)
- 1 MB of RAM
- 256 KB of ROM w/ full system monitor, OS, and 16-bit BASIC
- Glue logic moved to two 22V10 GALs
- 28L92 Dual UART providing two DB-9 serial ports
- 80 MHz Parallax Propeller for analog VGA video, stereo audio, and SPI
- ATmega328p for PS/2 keyboard/mouse and two NES-compatible game ports
- Dual 65C22 Versatile Interface Adapters
- SD card reader
- A user port
- A single expansion slot
When I started this project my goal was to produce another headless SBC similar to COLE-1, but with an expansion slot that would act as a platform for developing my custom CPLD-based video system. However it became apparent that I was trying to take too big of a leap there, and so I decided to add basic on-board video as an interim step.
My current prototype is scaled down from the final specs, since it’s implemented on solderless breadboards. It only runs at 2 MHz, and has only 512 KB of RAM, 32 KB of ROM, one VIA, and no ATmega. Much of this is just due to lack of space on the breadboard; as you can see I’m already spilling out onto additional boards, and all those long wire runs take their toll on stability, especially at higher speeds. My plan is to squeeze the ATmega in there somewhere to get a working keyboard port, and then move on to designing the PCB and building a full prototype.
In my next post I will dive into how I integrated the Propeller into my design.
