[Diy_efi] Continuing the chip switcher "problem"

Martin E martine001 at verizon.net
Mon Feb 14 23:53:36 GMT 2005


Marcello,

This chip the 74HC373 is a 'transparent latch'. The Q ouputs follow the D
inputs.
This is used for demultiplexing the bus Address's from the data. Mostlikely
its a 8 bitter in the ECU.

It typically does not drive the chip selects.
Although it may be used as  a buffer in transparent mode.

If you do latch the upper 2 bits use a true latch.

Cheers

----- Original Message ----- 
From: <mbelloli at speedymotorsports.com>
To: "A list for Do-It-Yourself EFI" <diy_efi at diy-efi.org>
Sent: Monday, February 14, 2005 5:15 PM
Subject: RE: [Diy_efi] Continuing the chip switcher "problem"


> Everyone,
>      I got a chance to play a bit this afternoon.  Maybe this piece of
> information will help.  When an eprom is installed in the ecu, you
> have to install a 74hc373 along with it.  These were both already in
> the ecu I am working with so didn't think that much about it.  Here
> is a link to a datasheet on that 3-state latch.
>
> http://www.jameco.com/wcsstore/Jameco/Products/ProdDS/45831.pdf
>
> Would this chip be supplying the signal to the not OE line? or the not CE
> line?  I'm going to take the ecu home tonight and do some probing.  I'm
> just thinking maybe this is the latch I need, and won't need anything
> else.
>
> Thanks,
>
> Marcello
>
>
>
>
>
> > Have you thought of using several chips the same size as the stock prom
in
> > parallel, and using flip-flops/logic to toggle the OE and CE lines to
> > enable
> > which chip you want?  That was another way I did it on my Buick GN
before
> > I
> > went to a single larger chip... The problem may lie in the fact that the
> > code is in the chip as well as the tables... GM was only tables...
Another
> > option is see if you cant build a small circuit to multiples one chip
with
> > the code and a flash for the tables and only change the tables...
> >
> >
> >> -----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 10:49 AM
> >> To: A list for Do-It-Yourself EFI
> >> Subject: Re: [Diy_efi] Continuing the chip switcher "problem"
> >>
> >> Will,
> >>      Unforunately the image is everything in one.  Both code
> >> and tables.
> >> I have put a link to the 29c010 on my webpage as well.
> >>        http://home.comcast.net/~hexibot43/ChipEnableLogic.htm
> >>
> >>      I had gone to the Pic Chip because I had a lot of other
> >> ideas I'd like to add as time goes by.  I wanted to be able
> >> to change to the code on the fly in one bank while running on
> >> another bank.  I could then switch it in after the changes
> >> and the checksum were calculated.
> >>  And I wanted to have a nice display because none of my
> >> friends understands what I am doing, but they understand
> >> plain english when it is in front of them.  I thought to
> >> maybe use a graphic display later, which would allow me to
> >> incorporate displaying the tables for fuel and spark.  I also
> >> want to later add datalogging capability.
> >>      I am thinking could I use this latch with my pic?  I
> >> would supply the new hi order address I would like to it, and
> >> when the time is right the latch would do the actual switch
> >> for me?  That way take the problem of the switching
> >> completely away from my pic.
> >>      I have another working computer that I have not modified
> >> at the shop.
> >>  I am going to go put my DSO on the Not OE line and see what I get.
> >>
> >> Thanks to everyone,
> >>
> >> Marcello
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> > Marcello,
> >> >
> >> > A further thought on this - can we assume that what you have in the
> >> > 29C010 is the fuel / ignition map ONLY, i.e. no executable
> >> code?  If
> >> > it contains both, then more complexity is needed, because you only
> >> > want to  assert the altered higher address lines when a fuel /
> >> > ignition lookup is being  performed.
> >> > But
> >> > you could still use the simple approach Bevan & I are
> >> advocating if
> >> > you have four images of the executable code as well, each
> >> with  their
> >> > own respective map but otherwise identical.
> >> >
> >> > Regards
> >> >
> >> > Will Cowell
> >> > _______________________________________________
> >> > diy_efi mailing list
> >> > diy_efi at diy-efi.org
> >> > http://lists.diy-efi.org/mailman/listinfo/diy_efi
> >> >
> >>
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> >>
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