19 Jun
2011
19 Jun
'11
8:21 p.m.
Thanks for the info, Dwight, Pete and others. That's handy. I'll digest it
while these EPROMS are in the post to me, and let the list know of any
progress.
Terry (Tez)
----- Original Message -----
From: "dwight elvey" <dkelvey at hotmail.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Sent: Monday, June 20, 2011 1:21 AM
Subject: RE: Sorcerer BASIC ROM-PAC ROM replacements
Date: Sun, 19 Jun 2011 13:25:37 +0100
From: pete at dunnington.plus.com
To:
Subject: Re: Sorcerer BASIC ROM-PAC ROM replacements
On 18/06/2011 23:00, Terry Stewart wrote:
---snip---
Hi
I prefer making an adapter. I use two stacked machine pin sockets
and rewire things to match up with the selects. I also always remove
the programming voltage. No sense blowing up a ROM because
I accidentally asked the programmer to write to it. Some programmers
leave the programming voltage on while reading as it is allowed
on that EPROM, so be careful. Always isolate the programmng
voltage pin.
Sometimes, jumpering isn't enough to get the EPROM to work.
The use needs another select that is high or low on the original
ROM that isn't there on the EPROM. For these I've been know
to take one of those tiny surface mount ICs to provide the logic
needed and hot glue it in the center of another machine pin socket.
One last thing. Make up a tag for the adpater you made to get
the programmer to read the ROM. I like to use a simple diagram
showing the levels of the select pins. Otherwise you end up with
a pile of duplicate adapters.
Also, I don't recommend bending a ROM pin enough to keep
it out of a programmers socket. These are usually ZIF type
sockets and you really have to bend it more than you'd want.
If it is a ZIF socket, a small folded piece of paper is usually
enough to isolate the pin without bending it.
Dwight
Well, I've spent a few hours today playing
with my Dual Powered Standard
Willem ROM burner.
It seems reasonably straightforward. I've managed to read the contents
of a few 27C256 EPROMS successfully. However, I couldn't read the
contents of the BASIC-PAC 2k masked ROMS? I'm sure I have all the
jumpers and switches right for a 2716, which I understand is an
equivalant EPROM chip .
A 2716 is an equivalent for 2K x 8 bit mask ROMs in the sense that the
capacity is the same, and the data and address lines are on the same
pins. However the the chip selects need not be. One of the
characteristics that can be "programmed" in the mask is the polarity of
the chip select pins. Also an EPROM has pins for programming voltages
as well as chip selects.
I did read on a website somewhere that some
masked ROMS could not be
read by some EPROM programmers. Do you think that's the case here?
No, you just need to deal with the chip select requirements. In this
case, the pins that might differ are pins 19, 20, and 21.
Pin 19 is A10 on most ROMs and EPROMs, but 12V on 3-rail 2716s. You're
unlikely to come across those, so it's unlikely to be of concern.
On mask ROMs, pin 20 is a chip select that can be active-high or
active-low; on 3-rail 2716 EPROMs it's the A10 address line, and on
single-rail 2716s, which are by far the most common, it's an active-low
chip select. The Exidy mask ROMs have it as an active-low so it's the
same as a common 2716.
Pin 21 is most likely to be the problem. On a 3-rail 2716 it's -5V.
More importantly, on mask ROMs it's a chip select that can be defined
active-low, active-high, or "don't care", while on single-rail 2716s
it's a programming voltage, and is set to +5V for reading.
That's what your programmer is probably doing, but the mask ROMs you
want to read use that pin as an active-low chip select. The solution is
to carefully bend pin 21 out sideways a little, just enough that it
doesn't go into the programmer socket. Then connect it to pin 12 (0V)
with a short test clip. Set up like that, you should be able to read
the ROM.