[Coco] Question about the PIA RAM Size input

[Darren A.]

>
>Also, important to note in the CoCo 3, it is pulled high with a 4.7k
>resistor and is connected to pb6 of the keyboard pia (since ramsize
>isn't used in CoCo 3). Perhaps a better pin to use would be pin 10 of
>the coco 3 rgb connector. it is connected to pb3 of the 6821 and is
>held high by a 4.7k resistor. it's intended purpose was to allow auto
>detection of an RGB monitor, but wasn't implemented for some reason. It
>is initially an input. on coco 1 and 2's it was connected to css of the
>6847, but since the coco 3 has no 6847, it was available for other use.
>Another method of control would be using the cassette relay to activate
>a circuit to control something else. -r
>
-

Actually, my reason for this had nothing to do with wanting to control any 
external circuit.  I simply wanted to ensure that when I read the PIA data 
register at $FF22, that all bits other than the least significant bit 
(Bit-Banger input) would be 0.

On a CoCo 1/2, the RAM Size input is the only other bit that is designated 
for input and would need to be reversed so I could force it to zero.

On a CoCo 3, I would also have to reverse the line which runs to the RGB 
connector. This shouldn't be a problem unless there is something unusual 
hooked up to pin 10 on that connector.

Darren

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