Hello
I finally decided to set up a blog to report the status of my work on a COC3+/COCO4 computer.
The heart of the design is John Kent's CPU09. It is a 6809 compatible processor and is not 100% timing wise compatible. There are opcodes that execute faster than the venerable old 6809. Still it is a good start and very usable.
Second is my own design of the GIME chip that is a major part of the COCO3 and any future designs that require backward compatibility.
What actually is the need for such a design? What drives this design is the perceived belief that there can be a niche for having an embedded COCO3 into modern functions. The current COCO3 board is far to large and cumbersome to use as a base for an embedded project. Instead a size more along the Arduino Mega boards with shields or wings would be better. Also I like the old venerable computer and my limited space does not allow me to setup my PC as well as a second monitor for a COCO3. Also the need to upgrade the monitor from a CGA to VGA at a minimum.
Design Concepts:
1) Modular design. Something like the Arduino style
2) The whole design will be in one or more FPGAs.
3) Make use of already available IPs that are not completely restricted in their use and modifications.
4) Use common free tools to develop the HDL and PCB layouts
5) Current thinking is to use XILINX Spartan 3 Series of FPGAs and their corresponding Webpack ISE software.
6) PCB software will be Eagle. It has more acceptance in the hobby market even though I think their auto-router lacks in ease of use and setup.
So what is done now:
1) The CPU from John Kent is ready and available.
2) Portion of the GIME chip is code and untested. All the control registers from $FF90 through $FFDF are coded as well as the control signals.
3) I have logic that interfaces the control register to the VGA section that will determine resolution and color depth. Initially this will be the standard COCO3 resolutions. Future inclusion will be higher resolutions and color depth. Need to walk before one runs.
4) Right now no PCBs are completed. Only concepts. The idea is a main board which will hold the CPU. A video board. Finally an IO board. I do have plans for a Floppy drive board. Not sure how relevant that is to modern designs. A MMC interface and a IDE interface is probably more necessary than a floppy disk interface. Even a USB interface is more relevant.
That is all for now.
More later
james
