Re: MM2114N RAM Replacement

Clay Cowgill wrote:

> > According to MAME this game uses a 6502 running at 1.5 MHz.
> > No way will a 450 nS RAM keep up with that. Go with the fast
> > part.
> >
> > (By the way, the NTE part is 300 nS).
> >
> That'll be fine. Running "balls-out" (not sure if that's a technical
> term or not ;-) a 450ns RAM could serve data up at about 2MHz
> (1/.000000450). Since the 6502 doesn't actually hit external memory
> every cycle the actual number is considerably less than 1.5MHz... 450's
> should work dandy.
>
> -Clay

There were a couple of reasons why I warned against using
450 nS RAM with a 1.5 MHz 6502. One of them is that
it's unlikely that they would wait-state a write (the 6502 will
NOT wait state a write cycle, so clock stretching would be
needed, and I know of no game that does that). The other
is that 6502 processors are very rough on memory timing.
A 450 nS RAM will have trouble even on a 1 MHz 6502
due to the way buss timing works on them. Everything
external to a 6502 happens during "phase 2", the last HALF
of a cycle. Addressing isn't guaranteed to be valid until the
start of phase 2 and data isn't guaranteed to be held past the
end of phase 2. Put those two things together and you are
probably violating timing on a 450 nS part, even with only a
1 MHz clock!

But, then again, a 2114 guaranteed for 450 nS is at that speed
when at MAXIMUM temperature. At lower temperatures it
will speed up (bipolar RAM is just the opposite).

I still recommend 300 nS (or better) RAM for this game.

As for Jameco and New York, the 200 nS 2114N-2L
low-power version is distributed as part of the Jim-Pak
line (catalog number 38981) and is sold by Central Electronics
in Utica, Radio Equipment Corp. in Buffalo, Trojan Electronic
Supply in Troy, and Unicorn Electronics, Inc. in Johnson City.

With any luck one of those will be close to where you live.
Received on Tue Mar 30 03:01:00 1999