Note: This project design is for use with OS-9, and so there is no support for BASIC.
After working on the by Color Computer to IDE interface I thought it would be much cleaner to avoid having a hard drive, external power supply, wires, etc. I started working on this idea in late 2002 and into 2003.
My first thought was to use a compact flash card, but it seemed complicated with all of the pins. I wanted something more simple to connect to the Color Computer. I looked into a new format called MMC or MultiMediaCard.
MMC Card example
Due to the complexity of the connection, I knew I would need something more advanced than discrete logic, as I had used on my IDE hard drive project. At the time I had been messing around with AVR microcontrollers from Atmel and so I investigated the use of their CPLD parts to design the logic needed. At the root of the project is a SPI that translates from serial bits to parallel bits required by the Coco. One more issue was that MMC cards needed 3.3V VS the 5V that is available from the Color Computer bus.
The part I chose for the project as an Atmel ATF1508ASL. The part had the I/O that I would need to interface two MMC cards and the Color Computer bus. Along with the CPLD there were two other parts required. One part was to convert from 5v to 3.3v and I chose to use a 74hc245 to do the conversion. For the necessary 3.3V I used a LM2937-2.5.
The board took some pretty severe wiring to complete, here is the result.
To connect to the Color Computer I used my IDE interface board with a 40 pin header.
OS9 Drivers in place. Note: The cards do not support booting to OS-9