[Coco] Question about the PIA RAM Size input

[Mike Pepe]

coco at yourdvd.net wrote:
> actually, depending on the coco (1 or 2) you have and the installed
> memory, depends on how it is jumpered, whether it be to gnd, vcc, pb6
> of the keyboard pia, etc. I wouldn't do it - say it is jumpered to gnd,
> and you output a logic 1 to it - or vice versa - probably wouldn't be
> good. Look over some schematics of various coco models - the jumpering
> scheme is different on the three coco 1 and 2 model schematics I just
> glanced at...r
> 

I'm going to negate you here a bit, but your logic is sound- I guess 
just to clarify things for Darren.

The PIA is a pretty robust device, it would survive having one of its 
outputs shorted to gnd/+5 pretty much indefinitely, at least according 
to the data sheet. However that's really not the issue- What do you 
intend to attach the output to is the better question. If whatever it is 
pulls the PIA line high or low when the PIA is in input mode - and that 
state matches the expected state - then you're golden. Obviously the 
loading of the output is fairly important. Again, it really depends on 
what you're attaching it to.

So, to clarify, if the expected state of the ram size input is 1, and 
when you disconnect the jumper and attach the device, read the PIA bit 
and if it's a 1, no issue. (yes, a gross simplification)

Now, if you patch the BASIC ROM to ignore the state of that PIA bit and 
correctly set the SAM registers for the memory size you have installed, 
what you do with that particular PIA bit is a don't-care scenario.

-Mike