[Diy_efi] Continuing the chip switcher "problem"

mbelloli at speedymotorsports.com mbelloli at speedymotorsports.com
Sun Feb 13 04:49:33 GMT 2005


     And perhaps I have created that noise.  My circuity is fairly simple,
but I did run a 6" jumper from the dip socket of the original eprom
out to a small board where my replacement chip is placed.  And I do
have a cable between my switcher, and this board.  Another possible
source of noise. I'm going to take a 27c256 that I've burned and
install it directly into the original socket.  And take my readings
from there.  And then I'll take some readinges with my circuity
installed.  Maybe with my circuity removed I'll see the real signal
I've been missing.

Marcello

> It may only care about the difference it has between it's VSS pin and
> the other pins, but if there is voltage or noise riding on the VSS, then
> the PCM is going to see that noise Plus the signals coming in and out of
> the chip superimposed... and that will play havoc with things.
>
>
> On Sat, 2005-02-12 at 19:51 -0500, mbelloli at speedymotorsports.com wrote:
>>      I'll do some checking again tomorrow with the DSO.  I'll take some
>> readings of my chassis ground to Vss.  And I'll take a reading from
>> Vcc to chassis ground, and to Vss.  It is baffling me.  The last car
>> I did confused my at first, but with some help I understood it.  This
>> one is not making any sense.  I figured the eeprom only knows the
>> difference between any pin, and its Vss pin.  So, if the waveform I
>> have is representative of that diffenence I would have my answer.
>> But it looks way wrong.  Maybe tomorrow I'll have the answer when I
>> check it again.  Thanks,  Marcello
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> > 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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