1024x8 bit BPROM & EPROM question

[Louis Baiani]

Thanks for all that info :O)  That sounds perfectly right.  Yes ns :O)  Oupsie.
Hey Do you think anyone would know of anything that would program a CY7C281/282
then?  I can still get these..it's if I can program them that is a problem.


Louis

Ludis Langens wrote:

> Louis Baiani wrote:
> >
> > Compared to the original 1kx8 BPROM found in my ECM (84 vehicles), do
> > you think a standard EPROM (1kx8 2708) would work?  You're talking
> > probably 450ms access time compared to 50ms with the actual blown fuses
> > in a BPROM.  I wonder if the ECM cares enough to really read this that
> > quickly or is it picky and that's why GM used BPROM.  Has anyone ever
> > suceeded in using a standard EPROM (if it's a fast EPROM, then that's
> > different).  Any feedback would be appreciated.
>
> I assume you mean 50ns and 450ns, not milliseconds.
>
> Here's why GM used bipolar PROMs in the earliest ECMs.  Back in 1980
> (when GM started using PROMs), the three supply voltage TMS2716 was king
> of the hill.  Single supply EPROMs as well as larger EPROMs were still
> in the "advance information" and "sampling" stages.  That was especially
> true a year or two earlier when GM had to commit to a design.
> Automotive temperature grades and speeds faster than 450 ns were likely
> unavailable in MOS EPROMs.  Further, EPROMs were expensive - they were
> meant for prototyping and extremely small production runs.
>
> Scot Sealander wrote:
> >
> > Louis Baiani wrote:
> >
> > > Anyone know where to get these?  ECG's 74S478 is not longer available I
> > > guess.  I wonder if a PROM/UV prom or ERPOM would work instead.  They
> > > refer to it as a DIL24 package I guess.
> >
> > If you put the program in 4 times, it should work in a 4kx8 EPROM, you
> > know, the 2732 series of EPROM's used in the C3 ECMs.  This is four
> > times as big, but it will probably still work.  I don't know what your
> > application does with the N/A pins that are used on the '32, so load it
> > four times.  One of the four ought to show up in the right place.
>
> Won't work.  There are reports that a Texas Instruments TMS2532 might
> work.  Lets analyze the situation.  There are four pins of interest.
> The twenty other pins are the same in all the 24 pin PROMs/EPROMs of interest.
>
> Here's how a CrossFire ECM connects the four pins:
>
>   21  A10 (from CPU)
>   20  ~CS (from 74138 decoder)
>   19  Unknown, possibly R/~W, possibly 5 volts
>   18  ROMEN (from edge card, normally pulled to 5 volts)
>
> Here's what these pins do on a 1KByte PROM:
>
>   21  ~E1
>   20  ~E2
>   19  E3
>   18  E4
>
> So, during a normal PROM read cycle, 18 and 19 are both high, 20 is low
> for addresses from 0x3000 through 0x37ff, and 21 contains the 0x0400
> address bit.  This means the PROM responds to addresses from 0x3000
> through 0x33ff - exactly the used range.  Data that I have suggests that
> 2KByte PROMs use pin 21 as their additional address input.  This means
> that GM designed the PCB for future upgrades.
>
> Now lets look at how 24 pin EPROMs use these four pins.  I've omitted
> the 2758 because it is just a half tested 2716.
>
>       2732  2716  TMS2532  TMS2516  TMS2508  TMS2716  TMS2708
>   21  A11   VPP   VPP      VPP      VPP      -5 V     -5 V
>   20  ~OE   ~OE   ~OE      ~OE      ~OE      A10      ~CS
>   19  A10   A10   A10      A10      NC       12 V     12 V
>   18  ~CE   ~CE   A11      ~CE      ~CE      ~CS      PGM
>
> >From this table, it can be seen that the Intel pinout devices will never
> be enabled in GM's circuit.  The smaller 5 volt only Texas Instruments
> pinout devices also won't enable.  And your crazy to even consider using
> a tripple supply EPROM.
>
> Of the 24 pin EPROM choices, only the TMS2532 might work as is.  The
> only problematic pin is 21 (VPP).  It is supposed to be held at 5 volts
> during normal EPROM operation.  I have a data sheet saying it may draw
> as much as 12 ma of current.  Perhaps this isn't an absolute
> requirement.  In any case, the PROM image would have to placed in the
> upper quarter of this EPROM.
>
> 74S478 isn't the only part number of a 1KByte PROM.  These are all
> equivalent:
>
>   MMI 6381
>   Fairchild 93451
>   Harris 7681
>   Intel 3628
>   Intersil 5618
>   Motorola MCM7681
>   National DM87S228
>   Raytheon 29631
>   Signetics N82S181
>   Texas Instruments TBP28S86
>   Texas Instruments SN74S478
>
> It should be possible to find small numbers of some of these chips.
>
> --
> Ludis Langens                               ludis (at) cruzers (dot) com
> Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/
>
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