RE: Bizarre Tailgunner (2) Experience

At 09:05 AM 8/21/97 -0700, you wrote:
>G'day folks,
>
>In my experience EPROM speed is quite important for Cinematronics games.
> I found out from my experience that I can slap any 2732 or larger EPROM
>into a Cinematronics board with no troubles! However, If I tried 2716
>only one in eight were fast enough (due to the random collection of
>2716's that I had access to). How does the speed of 2532's compare to
>2732's? I know I've used some 2532's in the past with no troubles.
>
>Again, I emphasize that my experience is limitted to whatever EPROMs
>that I've run across. Maybe I just always had fast EPROMs at my
>disposal?

Many of the C-CPU instructions executed in one 5mhz cycle, which would give
you 200ns access time -- way beyond the capabilities of the ROMs at the
time. By using two EPROMs and alternating back and forth between the two,
you can run at the same speed using only 400ns memory. Which is why
Cinematronics have EVEN and ODD ROMs. It doesn't have a 16 bit bus, but
instead by accessing alternate ROMs you can give the ROMs twice as long to
retrieve their data.
Still, if too many single cycled instructions are executed in a row you
would need 400ns memory, still too fast for most memory at the time, so
Larry (remember poor ol' Larry?) came up with a wait state generator that
will insert an extra cycle if ever the memory is accessed in less that three
cycles.
  
The design was clever and used a counter and a lookup PROM to determine when
a wait state is needed.

So that leaves you with the need for 600ns ROMs. Within the range of the
EPROMs of the day, most were rated between 450-550ns, but I can see some of
your older ones not even making this spec.

The newer EPROMs run much faster, and if you wanted you could defeat the
wait state generator, to to allow you to write more complicated games in the
future (now there's a market: Software that only runs on a C-CPU with the
wait states disabled!).

Disabling the wait state generator wouldn't effect the speed of the current
games since they're controlled using an external timer, not by counting
cycles (Well it might mess up the pretty sparkling sun in Space War, since
that was done using software timing.)

And there ya go, your dose of Arcade Trivia for today...

-Zonn
Received on Thu Aug 21 11:41:06 1997