[Diy_efi] Continuing the chip switcher "problem"

[mbelloli at speedymotorsports.com]

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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