[Diy_efi] Continuing the chip switcher "problem"

Sun Feb 13 00:55:19 GMT 2005

     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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