[Coco] Looking for joystick & hi-res joystick reference / theory manuals

Rick Ulland rickulland1 at gmail.com
Mon Oct 5 08:31:21 EDT 2020


IANADW (not a driver writer), but I just wrote up the hardware side of 
the hires interface in unnecessary detail, so I can tell you what is 
going into the CoCo, at least.

The hires interface accepts a timing pulse from the cassette out, this 
plus the joystick's output voltage creates a square wave who's pulse 
length represents joystick position. The CoCo only sees 0 and infinity 
(63), and the HiRes code needs to count or time this transition (as well 
as provide the cassout trigger pulse).

There is some overscan - on my bench the CoCo cursor doesn't move off 
the edge until the pulse has grown about 20%, and it's at far right at 
about 80%. That's great for mice, less desk space used. Not sure about 
other controllers.


On 10/5/20 4:54 AM, Walter Zambotti wrote:
> Hi guys
> I've got a week off and I'm trying to add the Tandy Hi-res joystick
> adapter to OVCC.
> Where can I find a theory of operation for the Hi-res joystick and also
> the standard joystick device?
> For the standard joystick I have been looking through the OVCC code and
> can see where the SDL joystick input routines (I wrote) get the host OS
> joystick values but I can't figure out where it places that joystick pot
> value into an emulated CoCo register.
> I assumed it would have written the value into $FF20 so it could be
> found later by what was running on the emulator, but it doesn't appear
> to be doing that!!!
> Walter

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