On Thu, 2 Jan 2003, Sellam Ismail wrote:
> On Thu, 2 Jan 2003, John Lawson wrote:
>
> > On Thu, 2 Jan 2003, Vintage Computer Festival wrote:
> >
> > > I've got the PICK CHECK signal from the reader going into CB2. I have a
> > > 1K resistor going from CB2 to ground.
> > ^^^^^^^^^^^
> > Try changing to 5K or even 10K (what I always use for pull ups/downs in
> > TTL work. I think you're burying the poor PICK CHECK signal. Actually
> > all the resistors oughta be 10K, IMHO.
>
> I'll certainly try that. But I'm wondering why that should be necessary
> when the 6522 data sheet says that particular pin is a TTL level output.
>
> Sellam Ismail Vintage Computer Festival
> ------------------------------------------------------------------------------
> International Man of Intrigue and Danger http://www.vintage.org
>
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>
I would think that you would be better off to use a pull-up resistor when
connecting a TTL output to a MOS input (even a supposedly TTL compatible MOS
input), since even totem-pole TTL outputs are weaker at pulling up than
down. A 1K _pullup_ is fine...
Peter Wallace
Received on Thu Jan 02 2003 - 14:08:00 GMT