[sebhc] H17 ROMS

Patrick Rigney patrick at vintagecomputermarketplace.com
Mon May 17 11:08:35 CDT 2004

> > The H17 ROM is a 2316 ROM; I haven't checked pin-outs
> > carefully, but I _think_ it can be duplicated with a 2716. My 
> > prom programmer (Data I/O System 19) doesn't want to read the 
> > 2316, but it can burn a 2716. If nobody responds sooner, I'll 
> > verify the compatability (or not) with the 2316 and try to 
> > burn a copy from my memory dump (which is what's posted to 
> > the archive).
> > 
> > Jack

Jack, continuing our off-line discussion on this very topic, I've made some
interesting discoveries.  Here's what I've found.

The only schematic I had handy that used a 2516 was for the SWTP MP-09 6809
CPU board from Mike Holley's site.  Interestingly, the text description of
the circuit says at first that the EPROM sockets on the board are 2716
compatible, but the parts listing for the board says those socket positions
take 2516 compatible EPROMs.  The schematic clearly shows, however, a
2716-compatible pinout.

I then started looking at the 2532 and 2732.  Unless the schematics I'm
looking at are wrong, the 2532 has a different pinout from the 2732--the
functions of pins 18 and 21 (a chip enable and A11) are transposed. I used
the charts below and the schematics for the AIM-65 and Commodore PET as a
reference (2332 consumers).  Both circuits show 2332s (masked ROM), but I've
used (recently, like this past weekend) a 2532 on an AIM-65 without any
issues, so I know the 2532 is a good replacement for the 2332, but using a
2732 takes rework.

In looking for the 2316/2516 however, I ran across some interesting
information.  Apparently a lot of the old pinball games used 2316s and
cousin 9316s, so they're a rich source.  I found a lot about changing
jumpers this way and that, and finally found a site that explained WHY there
are so many jumpers on boards that use them. Apparently, both the 2316 and
9316 had manufacture-time customer options for 2 or 3 enable lines and
active low or active high enables.  It went on to say (correctly?) that the
x316A parts are active high enables, and x316B are active low.  This makes
the x316A parts incompatible (directly) with the 2716.

Coincidentally, I'm holding in my hand an interesting little daughterboard
that I got in a box of stuff I bought on eBay a couple of weeks ago that was
advertised as "Electronic parts for HAM radio operator" (the photo clearly
showed many MOS parts including what turned out to be several gold/ceramic
6502s in original packaging, and indeed it's a treasure trove of old
computer stuff and few radio parts).  That board has a 2716 in a socket with
a 7404 next to it, and based on the above discovery, it appears it's a
2316A/9316A adapter.  Small world.  Following traces, this board inverts
plug pin 20 and puts it on pin 18 of the 2716, it pulls pin 21 on the 2716
high, and pin 21 on the plug is inverted and delivered to pin 20 on the
2716.  Plug pin 18 is not connected.

So, I know the 2332 and 2532 are pin-compatible.  If the schematic for the
MP-09 is correct, and the pinball site is correct, then (1) the 2516 and
2716 are pin-compatible; (2) the 2532 and 2732 are NOT pin-compatible; and
(3) the 2316/9316 and 2516/2716 MAY NOT be compatible due to
customer-selectable variations in manufacturing.  But I'll bet Heath's
choice was to use active low enables, which would make a 2716 work for the
2316.  I don't have a schematic here at my office, but maybe someone can
confirm that the H-17 ROM has two active low enables on pins 18 and 20, and
Vcc on pin 21?

FWIW, I found a couple of interesting EPROM cross reference documents on the
net somewhere, and saved them.  I've uploaded them to the SEBHC site (one is
a nicely produced PDF, the other is a GIF scan of someone's hand drawing).
The PDF shows the commonality between the 6116/6264/62256 RAMs and the
27xx(x) EPROMs.  There are also cool parts like the 28C64 and 28C256 EEPROMs
that pin out the same and don't require UV erasure to program.


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