[Diy_efi] Continuing the chip switcher "problem"

[Martin E]

Marcello,

Looks like your Vss isnt exactly gnd, Is the probe gnd lead tied to the
chassis or to the Vss pin on the Eprom? What is the DC between the Vss pin
and Chassis? Thats one ugly waveform ;)

There might also be some odd ball ground offset design. particulary for the
injector drivers so that the Fet gates get a negative voltage to turn off.

And Yes the OE is where the read strobe would be connected, unless by design
the OE is tied to gnd. This might be done if the Eprom is the only thing in
the memory map. The read strobe should still be availble on the Uc.

Cheers
----- Original Message ----- 
From: <mbelloli at speedymotorsports.com>
To: "A list for Do-It-Yourself EFI" <diy_efi at diy-efi.org>
Sent: Saturday, February 12, 2005 2:00 AM
Subject: Re: [Diy_efi] Continuing the chip switcher "problem"


>      I think I'm following what is being said.  Now here is a link to my
> web page with all the info on my chip switcher.
>           http://home.comcast.net/~hexibot43/ChipEnableLogic.htm
>      I was thinking that I should be doing the switching during the time
> that no read was occuring.  Now we're saying that I should do it
> immediately after a read occurs.  Does that mean when I see the
> moment of a read I immediately do my switch?  Whatever immediatley
> means.  I'm hoping everyone will look at the waveform I'm seeing on
> my Output Enable pin, and see if they can give me any insite.  I'm
> very confused by it.  I swear it never gets near ground.  Help me
> ObiWan your my only hope....Marcello
>
>
>
>
>
> > Martin,
> >
> > I absolutely agree.  There isn't a problem if normal good practice is
> > followed.  I used to be a hardware designer and would never think of
> > changing
> > addresses without "locking in" those changes to the read cycle.   The
> > address upper
> > bits (used for bank switching) should always be stable  during a read.
If
> > they aren't latched, there's likely to be  trouble.  And since it is so
> > simple
> > to do, any quad latch will do it, there  really seems no reason not to.
> > The
> > chip data sheets are available, I have  to assume - I'm no longer
working
> > as an
> > engineer.
> > Good luck and best wishes
> >
> > Will Cowell
> >
> >>Marcello,
> >>
> >>As an electrical engineer, I would say that it  would  be wise to Latch
> >> your
> >>bank switching bits on the rising edge  of the read strobe. This way the
> >>address will not change during a READ  (usually active low). Ugly things
> >> will
> >>happen and you may not meet the  setup and hold times for the Flash
> >> memory.
> >>Also if the bank switching  wires are 'long' you may be coupling in
noise
> >> to
> >>the ECM, as well as  switch bounce noise.
> >>
> >>cheers
> >>Martin
> >
> > ----- Original  Message -----
> > From: <mbelloli at speedymotorsports.com>
> > To:  <diy_efi at diy-efi.org>
> > Sent: Thursday, February 10, 2005 6:46  PM
> > Subject: [Diy_efi] Continuing the chip switcher problem
> >
> >
> >>  Hello Everyone,
> >>      I had asked the question eariler in  regards to creating a
multiple
> >> bank chip switcher for an ecm.   Everyone basically said I should be
> >> able to just switch the chip without  any regard for whether the chip
> >> is being accessed during the  switch.  I finally got my pic chip
> >> controller up and running.   I'm running at 20mhz, and when I do a
> >> switch I'm still getting a check  engine light.  2 out of three times.
> >>  Thinking about this, I  put the same exact bin in each of the banks
> >> of the chip, and still get  the same response.  Could it not be that
> >> I'm switching in the  middle of a read, and that is causing this
> >> problem???  What does  everyone think.  If I turn the car off, and do
> >> the switch no  problem.  I'm using this on a 1991 acura integra....had
> >> a 27c256 as  the base chip, and I'm using a 29c010 as the replacement.
> >>  I'm  controlling the highest two address lines as bank select for a
> >> total of  4 banks.
> >>      I'll put the info for chip changer on my  website, and add a link
> >> to
> >> it tonight.
> >>
> >>     Any ideas???
> >>
> >> Thanks,
> >>
> >>  Marcello
> >
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> >
>
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