M200 interfacing continues...

From: Sellam Ismail <foo_at_siconic.com>
Date: Fri Jan 3 02:40:01 2003

On Fri, 3 Jan 2003, Sean 'Captain Napalm' Conner wrote:

> > The problem I'm having now is timing out too quickly on the first column
> > read of the first card. According to the M200 docs I thought I had only
> > a few dozen microseconds to sense the first IM but it is timing out with
> > an 8-bit counter set to 255 and polling the IM signal in a loop that
> > takes about 14 cycles (14 * 255 = ~3500 cycles).
> It actually sounds like the timing is 6 milliseconds, not 6 uSecs as
> originally stated. If it is indeed 6 milliseconds, you then need to pause
> for 6,000 cycles.

Actually, it is indeed 6 uSecs. The problem I eventually had was a dodgy
input on the 6522. Once I moved it to another pin it started working.

Peter Wallace's suggestion of moving it to a latched input was the key.
Since the signal is usually too fast for the Apple to catch while it is
doing other processing, latching it enabled the Apple to catch it, after
which there was plenty of time (~2000 cycles) to play with the data before
the next column is read.

I have the Index Mark input on CA2 and it's working flawlessly.

I just ran a few batches of the different cards I am converting and
everything is coming out swimmingly.

Sellam Ismail Vintage Computer Festival
International Man of Intrigue and Danger http://www.vintage.org

 * Old computing resources for business and academia at www.VintageTech.com *
Received on Fri Jan 03 2003 - 02:40:01 GMT

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