On 15/04/2017, at 1:45 AM, Fred Cisin via cctalk <[email protected]> wrote:
> I had thought that both ends of the Screen printer cable would be 40 pin, 
> That's why I had speculated on Model 3.
> But I never spent $599 for one.
> (instead, I struggled with interfacing a DTC-300 HyType 1 serial printer)

I never had a Screen Printer either, but I don't think it would even be 
possible to use with a Model III.

I assumed the way it worked on the Model I was by either watching the CPU bus 
and sniffing writes to the video memory (mirroring to its own copy 
continuously), or reading the video memory when needed (trickier with 
synchronisation).

Unfortunately, despite the Model III having 50 pins instead of 40, 25 of them 
were ground and A0-A7 of the address lines were exposed. Even that was only 
enabled for IO ports via software first. The Model I was much for flexible for 
add-ons.

Scott.

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