7 Feb
2015
7 Feb
'15
11:20 a.m.
Pete Turnbull wrote:
On 06/02/2015 07:44, Holm Tiffe wrote:
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.
Regards,
Holm
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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