M200 interfacing continues...

From: J.C.Wren <jcwren_at_jcwren.com>
Date: Thu Jan 2 15:01:00 2003

        It has been my experience that any time you start seeing pulldown
resistors, you need to run away. Far far away. TTL and CMOS, with the
exception of certain parts, have very poor drive capability, but excellcent
sink capability. If he's really having a problem like this, then it may
call for an inverter, perhaps with a Schmidt triggered input.

        But pulldowns... Bad juju...

        --John

> -----Original Message-----
> From: cctalk-admin_at_classiccmp.org
> [mailto:cctalk-admin_at_classiccmp.org]On
> Behalf Of John Lawson
> Sent: Thursday, January 02, 2003 15:50
> To: Classic Computers Mailing List
> Subject: Re: M200 interfacing continues...
>
>
>
>
> On Thu, 2 Jan 2003, Peter C. Wallace wrote:
>
> >
> > The resting state (0) will be determined by the M200, With
> a pullup the signal
> > will be high when the M200 is not connected, but I doubt if
> that matters...
>
> Certainly you are correct in the generic case, and I would
> have thought
> so to. However: from speaking w/Sellam on the phone
> regarding this, it
> seems that M200 is not 'zeroing' that pin well, so I suggested
> pull-downs... without a resistor the pin floats around...
> not exactly
> sure on a molecular level whats going on, but it probaly has
> to do with
> competing power supplies... anyway, I'm curious to see if
> changing to 5K
> or 10K will solve the problem...
>
> But certainly this whole subject is producing a good deal
> of information
> which should prove useful to the next person who has a
> similar interfacing
> task!
>
> Cheers
>
> John
>
>
>
Received on Thu Jan 02 2003 - 15:01:00 GMT

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