[Diy_efi] Continuing the chip switcher "problem"

[Martin E]

Tek TDS1002 $995  List.

Cheers

----- Original Message ----- 
From: <mbelloli at speedymotorsports.com>
To: "A list for Do-It-Yourself EFI" <diy_efi at diy-efi.org>
Sent: Wednesday, February 16, 2005 4:00 PM
Subject: Re: [Diy_efi] Continuing the chip switcher "problem"


> To Everyone,
>      I am thinking about upgrading my DSO to something new.  I was looking
> at the Fluke 192, mostly because I can make payments on it.  Any
> comments.  I want to find something that is going to keep me up to
> speed for a while.  The fluke is about $2000....Is there something I
> can get for less money that would do a good if not better job.
>
> Thanks,
>
> Marcello
>
>
> >> I took a look at a datasheet for the 74xx374 and think I understand
> >> what is going on.  You put your new request of change of data in, and
> >> on the next positive slope of the clock, the old data will be
> >> switched to the new data.  So until the clock rises, the old data
> >> will be there.  And if I'm getting this right, the data is only read
> >> at the negative transition of the clock?  So you will have done the
> >> change during the time you aren't performing a read.  And the system
> >> will be no wiser.  Even if an instruction was in being read, and not
> >> data from the chip it will still be transparent.  Hence the
> >> Transparent latch name.  Could you look at the Not PSEN signal I've
> >> taken from the MCU at pin 23, and the Not OE pin as I've recorded
> >> them on my webpage.
> >
> > Your analysis of the operation is correct. I looked at your traces, but
> > none of these are usable, due to scope limitations.
> >
> >>            http://home.comcast.net/~hexibot43/Waveforms.htm
> >>      Is it possible that although the signal never reaches Vss or
ground
> >> the computer could still be reading it as Vss or logic state low?  Is
> >> it possible that when it reaches the 2.5 v median point the computer
> >> accepts that as ground?
> >
> > Apparently your DSO does have an alias filter, and due to this you see
> > only the average of the signal when it is changing at at a much higher
> > rate than your scope can handle. A better (higher sample rate or
> > bandwidth) scope will surely show the signals switching between ground
> > and Vss/Vcc/whatever.
> >
> > --
> > Robert W. Hughes (Bob)
> > BackYard Engineering
> > 29:40.237N, 95:28.726W or perhaps 30:55.265N, 95:20.590W
> > Houston, Texas "The city with too much Oxygen"
> > rwhughe at oplink.net
> >
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> >
>
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