Re: 1351 mouse and the VIC20

Date: Thu, 27 Apr 2017 12:15:30 +0200
Message-ID: <11415497.sGx2h3cR3c@rakete>
On Thursday 27 April 2017, 01:46:35 Jim Brain <> wrote:
> On 4/27/2017 1:02 AM, wrote:
> > mmmh there must be something else that is different - if that'd be the
> > only
> > difference the 1351 should still produce *some* values, right?
> Since I didn't want to promote bad information, I fired up the scope.
> It looks like it uses the same 512 cycles (506uS per ADC cycle,
> according to my NTSC VIC-20), but holds the line low only for 64uS, and
> then releases the line for the remaining 448uS.
> The 64, on the other hand, drags the line low for 256 cycles, and then
> releases it for 256 cycles.
> The mouse operates by taking the value it wishes to send, adds 256 to
> it, waits for that falling edge of POTX, waits that many 1uS cycles, and
> then pulls the line high.  Lather, rinse, repeat.
> The ADC has to start sampling the comparator immediately after it
> releases the line.    Assuming the VIC samples 256 cycles, it must
> sample from 64uS to 319uS, while the 64 samples from 256 to 511uS.  Of
> the 64 256-511uS, the 1351 only starts pulling the line hi at 256+64uS =
> 320uS. Thus, the 1351 never pulls the line high at any time the VIC-20
> ADCs are scanning the line.

aaah i see. that makes sense. thank you!


Usability:Simplify the Solution  Design:Simplify the Problem

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Received on 2017-04-27 11:00:03

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