[Coco] CoCo 128-column text mode

[Nick Marentes]

On 8/01/2015 6:06 AM, William Astle wrote:
> Theoretically, it would allow for 256 columns in a text mode with no 
> attributes (1 byte per character). Bit 7 of FF9F actually forces the 
> line width to 256 bytes instead of whatever the actual screen width is 
> set to (each line starts 256 bytes past the previous one).
>

In graphics mode, bit 7 is the Enable bit so that's 128 combinations so 
to extend to 256 bytes wide, the minimum increment is 2 bytes.

I other words, the horizontal scrolling is 2 bytes or 4 graphic pixels 
at a time.

I haven't played with the text mode but I think a similar restriction 
occurs here.

It probably allows single character scrolling across 128 columns with 
text attributes on.

Nick