TECH: PROMS, EPROMS, etc.

[Metahugh]

I've spent a bit of time reading Clays guides and I haven't found an
answer to this question. I know the difference between the different
ROM types:

PROM: Programmable ROM
EPROM: Erasable Programmable Rom

But what I am trying to figure out is what the extra PROMS on the
System 4 cpu board that came in my Time Warp are for.

There are two flipper ROMs, 1 game rom and three unmarked roms on the
board. What do the three unmarked ROMS do? The glue on the top of
these chips is obscuring the chip type so I can't tell what type they
are to see if they are different from the flipper and game rom chips.
They do look a bit different, they are about twice the height of the
flipper and game roms.

Also can an EPROM be used interchangably with a PROM? I know proms are
write once and EPROMs are write twice, but if they can't be used
interchangeably then why not? Are they different sizes? (i.e. 2532 vs.
2732)

Thanks!

Hugh
metahugh at comcast dot net

[firebir...@yahoo.com]

Lose the upper three keep the flipper roms and replace the third on
the pottom next to the flipper rom with a eprom from the williams site

[c...@provide.net]

It's all explained in the repair guides.
the original PROMs are 512 byte ROMs.
These can be replaced with
2716 EPROMs which hold 2048 bytes. So you
put in EPROMs, change a couple jumpers,
and replace all the PROMs with fewer
EPROMs. This saves the number of
SCANBE sockets that need to be replaced
since the total chip count is less with
2716 EPROMs.

[Metahugh]

Thanks for the replies.

Okay, I think I'm getting it. So I took one of the green labels off
one of my Flipper roms, at I see the stamp 9361B - This is masked rom
correct? And if I needed a replacement then I could get a 2716 with
the same image burned to it?

My game ROM, and two of the other three ROMs I was inquiring about have
the following markings:

6341 11
S11203 8022

Are these PROMS? I can't find anything based on the markings.

But ultimately I will have three EPROMS: Two flipper 2716s and one
game 2716.

Thanks,

Hugh

The third has no markings at all.

[John Wart, jr]

Correct, that is a masked ROM.

You can replace it with a 2716.

The others sound like masked ROMS or PROMS to me too.

A lot of the time, the legs rot on these chips. Chances are, if you remove
them, the legs might actually crumble.

3 2716's is the best way to go. Replace the awful scanbe sockets with open
frame machined sockets or SIP strips, and get 2716's in there. You might
also consider programming one of Leon's test chips for your era of machine -
http://home.scarlet.be/~pb007911/williams/ewilliams.htm

If you need any of these programmed, let me know and I will get you set up.

Glad to see you're giving this game a shot at being saved!

--
http://www.myhomegameroom.com

"Metahugh" <meta...@comcast.net> wrote in message
news:1135228894.0...@g44g2000cwa.googlegroups.com...

[Metahugh]

Thanks John.

So bascially the 3 extra roms on my board are installed for no reason.
I should only have 3 roms installed on the CPU board, the two flipper
ROMs and the one Game ROM.

Since I don't know the status of my ROMS and I don't own a programmer
(yet =) ) I will be in contact with you to get a fresh set, if you do
Sys 6 rom sets. I checked your website but it says "Coming Soon".

I'm definitely going full steam on it. Making up a parts list right
now so I can order it all at once.

Thanks,

[John Wart, jr]

The 3 extra chips are neccesary in your configuration unless you upgrade to
eproms. The CPU prom is a 512 bytes and the 3 other chips are 512 bytes. A
2716 eprom holds 2048 bytes, 4x the capacity of the CPU PROM or the other 3
proms. WMS went with those most likely as a cost cutting move - you can
replace 6 chips with 3 eproms - that is the preferred direction.

--
http://www.myhomegameroom.com

"Metahugh" <meta...@comcast.net> wrote in message

news:1135267295.7...@g44g2000cwa.googlegroups.com...

[Metahugh]

Ah, now I finally understand.

The roms on IPDB are for 2716s. Since the game rom is 2048 bytes in
size, and since the proms used from the factory only held 512 bytes the
game rom itself was split among four proms. Putting the 2716 allows us
to consolidate the 4 proms into one EPROM. Thus only 3 roms installed.

If you are using the original PROMS does it matter which socket it's
in? I assume that back in the day if an OP had a ROM issue they would
just replace the PROMS with EPROMS and skip the whole PROM dealio.

I always wondered why there was only 1 game rom in the ROM set on IPDB.
It's interesting that Williams designed it to go either way.

[firebir...@yahoo.com]

Hugh,
no Pinball Manufacturer wanted to pay a Premium price for Eproms which
had just emerged onto the market. Masked Roms and Bipolar Proms were
the cheapest way to mass produce Memory IC's and both Game makers
went that route at first. Bally chose masked roms and so did Williams.
In a shortage bind or to get a new game to market sooner, Williams also
used Bipolar Proms.
Three smaller capacity, inexpensive Bipolar Proms could be used in the
top 3 sockets in place of a Masked Rom (or 2716 Eprom) at IC14. That
was easily accomplished by having the same address for IC 20, 21, 26 as
IC14

[Dallas Overturf]

Yes that's correct (though I believe you meant 9316B). In fact the
william's9316B Masked ROM is
directly pin for pin READ compatible with a 2716 EPROM. Note I say read
compatible as the 9316B is not programmable.
So from the pinball machine's standpoint they are the same.

Note: if you have trouble finding a 2716 you can use a 2732 in it's place
provided that you program the upper half.
Lots of folks here seem more comfortable programming both halves of a 2732
with the same data repeated; however
technically you only need to write the2716 image into the upper half to make
it plug in compatible.

Regards and Merry
Christmas to all, Dallas...

--
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"Metahugh" <meta...@comcast.net> wrote in message

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