11/23 clock issue

Holm Tiffe holm at freibergnet.de
Sat Feb 7 13:20:48 CST 2015

Pete Turnbull wrote:

> On 06/02/2015 07:44, Holm Tiffe wrote:
> >You don't ned no pullup for +5. All open TTL inputs are reading High w/o
> >any pullup.
> Yeah.  So someone at Commodore thought when they designed one version of 
> the PET.  We had a few that erratically misbehaved.  It turned out that 
> one input on a 74LS00 (I think it was) was floating, and switching noise 
> made it erratic.  Floating inputs place the internal circuitry in an 
> intermediate state, can cause increased current draw, typically slow the 
> device down by increasing switching times, and can cause misbehaviour.
> TTL is supposed to have a 1K pullup (to limit possible transients); 
> LSTTL can be directly connected to Vcc.
> -- 
> Pete
> Pete Turnbull

Yes Pete, not all People over here are totally braindead.

I've told him that he can leave out the +5V Connection for testing
purposes, for nothing other.
That has nothing todo with your Commodore problem.


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