Re: Tempest board rev.

Ah, well, it is fairly simple once you understand the addressing. On your
board, there are, say for simplicity two 2716's. Now the hardware person
was a bit creative and wanted to take advantage of the cheaper 2532's (when
they become available - remember this is 1980ish)) and hardwires the board
so that the first socket has A11 as the chip enable for the 1st 2716, and
inverts A11 to use as the chip enable for the second 2716. Now when you use
the chip select you have it cover a 1K window instead of 1/2K and for the
first half of the 1K A11 is LOW thus 2716 #1 is enabled and 2716 #2 is
disabled because it sees inverted A11 or HIGH. Now for the upper half of
the 1K window, you then toggle A11 high, this disables 2716 #1, and enables
2716 #2. Now when the 2532's drop in price to rival the 2716's you just
drop them in, they program faster and fewer assembly steps for the
manufacturer. Or if 2716's aren't available or whatever...

On your Tempest they just had a bunch of 2716 sockets that were wired to
A11 and the second bunch wired to inverted A11, thus when you stuff in the
2532's, you just use the first bunch with regular A11.

You will see some games that had jumpers in place that would allow you to
run MANY different types and sizes of ROM memory - Midway motherboards
spring to mind as an example, plus Bally pinball MPU's.

Clear?

John :-#)#

At 12:59 PM 4/1/2000 , Tek wrote:
>Yes, but how does the board know? Probably I'm being stoopid, but I still
>cannot
>see it?
>
>Cya !
>
>John Robertson wrote:
> >
> > If your version is using 2532's, then the A11 of the 2532 is the old
> > ChipSelect on the 2716, which was often A11 (like Pacman, Tempest and other
> > games)
> >
> > John :-#)#
> >
> > At 09:12 AM 4/1/2000 , Tek wrote:
> > >Hi guys-
> > >
> > >I was wondering, is a newer Tempest board with only half of the ROMS
> different
> > >from the 'normal' one?
> > >
> > >As far as I could see the address decoder is still the same, but how
> does it
> > >know the data of each second
> > >ROM is in the first location?
> > >
> > >Cya !
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  John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
  Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
  http://www.flippers.com
         "Old pinballers never die, they just flip out."

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Received on Sat Apr 1 17:28:26 2000