[Coco] Question about the PIA RAM Size input

coco at yourdvd.net coco at yourdvd.net
Mon Apr 30 11:57:23 EDT 2007

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

> -------- Original Message --------
> Subject: [Coco] Question about the PIA RAM Size input
> From: "Darren A." <darccml at hotmail.com>
> Date: Mon, April 30, 2007 8:27 am
> To: coco at maltedmedia.com
> Hi all,
> Does anyone know if any harm can be done by reprogramming the Data
> Direction 
> Register of PIA 2 such that the RAM Size input becomes an output?  Since 
> this line is often jumpered to either GND or +5V, what happens when
> the PIA 
> is trying to drive the line?
> The RAM Size input is on the 'B' side of the PIA, and the 6821 datasheet 
> says:
> "As outputs, these lines are compatible with standard TTL and may also
> be 
> used as a source of at least one milliampere to directly drive the
> base of a 
> transistor switch."
> Darren
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