[Diy_efi] Continuing the chip switcher "problem"
Bevan Weiss
kaizen__ at hotmail.com
Mon Feb 14 05:09:22 GMT 2005
Hey Marcello,
Why are you using a PIC chip to do the change? It seems like a bit of
processor overkill.
I'd just use a couple of clocked D type flip-flops, connect the clk input to
the same source as the clk on the ROM (make sure the trace lengths are about
the same if at all possible), then connect up the flip flop inputs to your
switches. Place some filtering on the input to the flip flops also (a
simple parallel RC should suffice) to remove some switching noise.
That should do the trick...
The outputs from the flip flops can directly drive the high address pins.
I'm really not sure why you'd be getting a check engine light problem etc.
I'd like you to just make sure that the CE trace is ok, and that you haven't
got anything attempting to drive it that you've added. Generally CE should
always be held low if that device is the only thing on the bus. OE would
normally be the pin that is toggled, as it tristates the output pins of the
ROM.
A ROM is like a clocked state machine. It's not super intelligent. You
apply an address, on the next clock cycle it looks it up and outputs
whatever data corresponds to that address. If OE is held high (cause
normally it's actually NOT OE or OE BAR however you want to say it) then the
output drivers are simply tristated. If the CE pin is held high then the
entire chip can actually shut down and no address decoding etc is performed.
Hence most ROM chips have a minimum time after the assertion of CE before
any valid data will be output, this time is always at least equal (normally
more) to the time taken for valid data to be presented after the assertion
of OE.
Regards,
Bevan
-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On
Behalf Of mbelloli at speedymotorsports.com
Sent: Monday, February 14, 2005 5:44 PM
To: A list for Do-It-Yourself EFI
Subject: Re: [Diy_efi] Continuing the chip switcher "problem"
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
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>> >> >
>> >>
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