[Diy_efi] Continuing the chip switcher "problem"
mbelloli at speedymotorsports.com
mbelloli at speedymotorsports.com
Mon Feb 14 04:46:11 GMT 2005
Ok, I finally got a chance later in the day to take some snapshots of
the waveforms on some of the lines on my AT29C010. I'm starting to
wonder about my DSO. It is a 5MegaSample unit, and the smallest time
setting is 5microsecs. And this is the setting I'm having to take
most of my readings. I wondering if it is really capable of
displaying true waveforms at the extreme limit of its setting. I
just can't figure why all the other pins I'm looking at on the chip
look reasonable. The only one that is giving me trouble is the one I
need to figure out.
http://home.comcast.net/~hexibot43/Waveforms.htm
Any ideas? 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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>> >> > diy_efi at diy-efi.org
>> >> > http://lists.diy-efi.org/mailman/listinfo/diy_efi
>> >> >
>> >>
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