[Coco] GIME text modes and font data

[jdaggett at gate.net]

On 4 Sep 2012 at 3:04, John Kent wrote:

> I'm sure most people on the list know all this.
> I'm reasonably familiar with the chips in the CoCo 1 & 2, although I'm not
> really up with all the registers in the GIME chip.

The GIME chip is not 100% backward compatible with the 6847/6883 combo. There are 
semigraphics modes that are not supported at least in software. I also think not in hardware. 

On the COCO1/2 the SAM chip generates the clocks to the MPU and the VDG clock. The 
VDG chip does have an onboard address generator for video memory access but is limited to 
only 13 bits or 8K of video memory. The VDG syncs the SAM chip for HS and VS and 
address timing. Similar happens inside the GIME as this has been integrated into one chip.

james