17 Sep
2007
17 Sep
'07
3:34 a.m.
I was happy to find earlier today that while I gave away most of my
tubes of chips and other parts about 3 years ago as I wasn't doing
anything with chips, I still have a 4 partial tubes of 27256's and
27C256's. IIRC, thankfully I'd thought they might be useful to hang
onto.
So the question of the minute is this, is it possible to substitute a
27C256 for a smaller 27C128?
If so I should have all the pieces I need for the first project with
the exception of the EPROM programmer and EPROM eraser.
Zane
--
| Zane H. Healy | UNIX Systems Administrator |
| healyzh at aracnet.com (primary) | OpenVMS Enthusiast |
| MONK::HEALYZH (DECnet) | Classic Computer Collector |
+----------------------------------+----------------------------+
| Empire of the Petal Throne and Traveller Role Playing, |
| PDP-10 Emulation and Zane's Computer Museum. |
| http://www.aracnet.com/~healyzh/ |
3:41 a.m.
So the question of the minute is this, is it
possible to substitute a
27C256 for a smaller 27C128?
Sure is. The pinout is nearly the same, save for pin
27. On the 128, it's the program voltage pin, but on
the 256 it's an address line. When programming your
chip, put your data in both banks (i.e., put it in
twice - copy your file and cat the two together into
one file) and burn that to the chip, being sure to
tell your programmer the truth about the chip. Then,
when you put it into the circuit, be sure that pin 27
is tied either high or low - not left floating.
-Ian
3:55 a.m.
On 16 Sep 2007 at 19:34, Zane H. Healy wrote:
So the question of the minute is this, is it possible
to substitute a
27C256 for a smaller 27C128?
For reading, sure. The difference is pin 27--PGM/ (program enable/)
in the 128 and A14 in the 256. So program your data into the upper
half of the 256 (or just program two copies of it--then it doesn't
matter if pin 27 is high or low).
Cheers,
Chuck
4:53 a.m.
So the question of the minute is this, is it possible
to substitute a
27C256 for a smaller 27C128?
IIRC the difference between a 27256 and a 27128 is that 128 puts VPP
on pin 1 - this is normally held at +5V for read applications. The
256 puts A14 on pin 1.
So a 256 will usually work as a 128 (reading - programming is
different) however you will most likely have to program your
code into the TOP half of the 27256.
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Collector of vintage computing equipment:
http://www.classiccmp.org/dunfield/index.html
5 a.m.
So the
question of the minute is this, is it possible to substitute a
27C256 for a smaller 27C128?
IIRC the difference between a 27256 and a 27128 is that 128 puts VPP
on pin 1 - this is normally held at +5V for read applications. The
256 puts A14 on pin 1.
So a 256 will usually work as a 128 (reading - programming is
different) however you will most likely have to program your
code into the TOP half of the 27256.
5 a.m.
At 11:00 PM -0500 9/16/07, Dave Dunfield wrote:
Mirroring in both halfs is always safe, or do what I
do
and put a jumper on the extra address pin - lets you have
two selectable ROMS (nor application and a debugger in
my case usually).
This is actually my end target, though I'll be using switches rather
than jumpers to select the version I want. I'll have to get the
datasheets and pay close attention to the pinouts when building the
adapters for the ones that are supposed to use the 27128.
Zane
--
| Zane H. Healy | UNIX Systems Administrator |
| healyzh at aracnet.com (primary) | OpenVMS Enthusiast |
| MONK::HEALYZH (DECnet) | Classic Computer Collector |
+----------------------------------+----------------------------+
| Empire of the Petal Throne and Traveller Role Playing, |
| PDP-10 Emulation and Zane's Computer Museum. |
| http://www.aracnet.com/~healyzh/ |
7 a.m.
On Sep 16, 2007, at 10:34 PM, Zane H. Healy wrote:
I was happy to find earlier today that while I gave
away most of my
tubes of chips and other parts about 3 years ago as I wasn't doing
anything with chips, I still have a 4 partial tubes of 27256's and
27C256's. IIRC, thankfully I'd thought they might be useful to
hang onto.
So the question of the minute is this, is it possible to substitute
a 27C256 for a smaller 27C128?
This may help:
http://www.neurotica.com/misc/eprom.png
I don't recall where I got it, but it has been *extremely* handy.
Whoever drew it had a damn good idea there.
-Dave
--
Dave McGuire
Port Charlotte, FL
Farewell Ophelia, 9/22/1991 - 7/25/2007
8:37 a.m.
This may help:
http://www.neurotica.com/misc/eprom.png
Some more help (recommended):
http://www.tabajara-labs.com.br/temp/tabeprom.gif
All eprom pinouts up to 27C080
(this is the ELNEC rom emulators' table which sits on the help file,
converted to a gif. Buy ELNEC products! :D)
Greetings from Brazil,
Alexandre Souza
21 Sep
21 Sep
8:44 a.m.
On Sep 17, 2007, at 3:37 AM, Alexandre Souza wrote:
Oh that is an extremely handy little GIF file! Thanks!
-Dave
--
Dave McGuire
Port Charlotte, FL
Farewell Ophelia, 9/22/1991 - 7/25/2007
This may
help:
http://www.neurotica.com/misc/eprom.png
Some more help (recommended):
http://www.tabajara-labs.com.br/temp/tabeprom.gif
All eprom pinouts up to 27C080
(this is the ELNEC rom emulators' table which sits on the help
file, converted to a gif. Buy ELNEC products! :D) 
17 Sep
17 Sep
4:13 p.m.
On Monday 17 September 2007 02:00, Dave McGuire wrote:
On Sep 16, 2007, at 10:34 PM, Zane H. Healy wrote:
Yes indeed! The closest I came to that was drawing the pinouts of a bunch of
them on the same page, along with some bytewide RAM parts...
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
I was happy to find earlier today that while I
gave away most of my
tubes of chips and other parts about 3 years ago as I wasn't doing
anything with chips, I still have a 4 partial tubes of 27256's and
27C256's. IIRC, thankfully I'd thought they might be useful to
hang onto.
So the question of the minute is this, is it possible to substitute
a 27C256 for a smaller 27C128?
This may help:
http://www.neurotica.com/misc/eprom.png
I don't recall where I got it, but it has been *extremely* handy.
Whoever drew it had a damn good idea there.
-Dave 
11:41 p.m.
So the question of the minute is this, is it possible
to substitute a
27C256 for a smaller 27C128?
The only real difference betwen those 2 parts is that the former has
twice as many locatiuons, and therefore 1 extra address pin.
There's nothing to stop you holding any of the address pins in a contant
logic state for all time. So if you program the 16K byte image in the
first half of a 27256 and hold the A14 pin low, it'll behave as a 27128.
Or program the image in the second hald and hold A14 high.
Or, of course, program 2 images into the chip and select between them
with a jumper conencted to the A14 pin.
But please don't just program the same image into both halves of the
27156 and leave A14 floating, assuming it'll always apprar as a 0 or a 1
to the chip, and since the 2 halves contain the same data, it doesn't
matter which it appears as. You _will_ have hard-to-find glitches if you
do somehting like that.
Other than the A14 input, the pinouts of the 2 devices are much the same
in read mode. So there's not even mouch PCB modification to do.
Also, IIRC, the pinout for programming a 27128 and a 27256 are rather
more different, with Vpp moving to a different pin. But if you use a
commercial programmer, that's taken care of.
-tony
18 Sep
18 Sep
12:45 a.m.
On Monday 17 September 2007 18:41, Tony Duell wrote:
> So the question of the minute is this, is it
possible to substitute a
> 27C256 for a smaller 27C128?
But please don't just program the same image into
both halves of the
27156 and leave A14 floating, assuming it'll always apprar as a 0 or a 1
to the chip, and since the 2 halves contain the same data, it doesn't
matter which it appears as. You _will_ have hard-to-find glitches if you
do somehting like that.
I would've thought so too...
Particularly with CMOS parts.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
6326
days inactive
6330
days old
12 comments
8 participants
participants (8)
-
alexandre-listas＠e-secure.com.br -
ard＠p850ug1.demon.co.uk -
cclist＠sydex.com -
dave06a＠dunfield.com -
healyzh＠aracnet.com -
ian_primus＠yahoo.com -
mcguire＠neurotica.com -
rtellason＠verizon.net