Finding 2732A eprom, or alternatives

[injb]

I have a board that uses an Intel 2732A eprom that I'd like to reprogram. I want to be able to try out a few variations quickly, so I either need a flash eprom chip or several UV erasable chips. With a flash chip I think I'd still have to make an adapter, so I was thinking of looking for a few 2732A UV eproms. It turns out they're being sold "brand new" cheaply in batches of 10 on ebay[1]

I presume these must be knock offs, right? Does anyone know if they are any good? If they are lower quality, what kind of problems might I run into?


[1] https://www.ebay.com/itm/10PCS-M2732A-2F1-M2732A-EPROMs-ST-DIP24-TOP-QUALITY/331766017987?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20131003132420%26meid%3D87a7e04791eb48c1a5542949246c5c57%26pid%3D100005%26rk%3D2%26rkt%3D12%26mehot%3Dpf%26sd%3D133398989956%26itm%3D331766017987%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWeb%26brand%3DUnbranded&_trksid=p2047675.c100005.m1851

[oPossum]

They will be genuine used chips. Probably cleaned up and possibly remarked.

[james_s]

You can easily use a modern 5V parallel flash chip or EEPROM with an adapter, that'll be way faster than using UV EPROMs.

[injb]

You can easily use a modern 5V parallel flash chip or EEPROM with an adapter, that'll be way faster than using UV EPROMs.

Do you where I can get an adapter for the 2732A to a flash chip? That would be ideal, but I haven't been able to find one.

[luiHS]

One option is to replace the 2732 with one of higher capacity from 2764 to 27512.

The 4 extra pins you connect according to the attached drawing. For example if you use a 27512 (which will be easier to locate than a 2732), you connect pins 1, 2 and 27 to GND, and 28 to +5v. Pins 1, 2, 27 and 28 are not used, the new chip you connect to your circuit from pin3, as if it were pin1 of the 2732.

If you prefer replace Eprom by Flash, a TSOP to DIP adapter you can order it on Aliexpress.

[TomS_]

ATMEL 28C64 (common) is an 64kbit/8kbyte EEPROM in a DIP28 package, and should have a very similar pinout to the existing ROM. Probably one address pin needs to be tied to ground (or tried high and your code stored in the upper half) but it shouldn't be hard to work out by doing a side by side comparison of the two.

IIRC the Vpp pin on smaller ROMs ends up being shared with an address pin on larger ones, you may need to dive into the schematic or do a little probing on the board to see what voltage level it's at.

Flash based EEPROMs I tend to only find in larger sizes like 1Mbit+, and usually in DIP32, but perhaps a bit more digging around would find something smaller.

Price wise I find that flash < 28C64 < UV erasable EPROM.

[james_s]

You can easily use a modern 5V parallel flash chip or EEPROM with an adapter, that'll be way faster than using UV EPROMs.

Do you where I can get an adapter for the 2732A to a flash chip? That would be ideal, but I haven't been able to find one.

Just make one, all you need is a bit of protoboard, some machined pin header strips and a socket for whatever chip you want to use.

[injb]

ATMEL 28C64 (common) is an 64kbit/8kbyte EEPROM in a DIP28 package, and should have a very similar pinout to the existing ROM. Probably one address pin needs to be tied to ground (or tried high and your code stored in the upper half) but it shouldn't be hard to work out by doing a side by side comparison of the two.

IIRC the Vpp pin on smaller ROMs ends up being shared with an address pin on larger ones, you may need to dive into the schematic or do a little probing on the board to see what voltage level it's at.

Flash based EEPROMs I tend to only find in larger sizes like 1Mbit+, and usually in DIP32, but perhaps a bit more digging around would find something smaller.

Price wise I find that flash < 28C64 < UV erasable EPROM.

Thanks - actually I didn't realize that there was a difference between flash and eeprom!

[up8051]

I think the best solution will be "EPROM Emulator"
For example "memSIM2 - EPROM Emulator" available on  Ebay.

[injb]

You can easily use a modern 5V parallel flash chip or EEPROM with an adapter, that'll be way faster than using UV EPROMs.

Do you where I can get an adapter for the 2732A to a flash chip? That would be ideal, but I haven't been able to find one.

Just make one, all you need is a bit of protoboard, some machined pin header strips and a socket for whatever chip you want to use.

This might be a stupid question - I got some prototype board, and male and female headers, but then I realized that the header pins won't fit into the existing eprom socket. Is this what you meant by "machined"? Could you give me any tips on how exactly to make them fit?

[oPossum]

To fit into IC sockets you want round machined pin headers that are 0.018 inch (0.46 mm) on one side.

[injb]

To fit into IC sockets you want round machined pin headers that are 0.018 inch (0.46 mm) on one side.

Thanks, I'll have to find some of those. For now I think I've figured out a way I can make it work: the female headers do fit in the socket. It doesn't feel perfect but I think it'll work without damaging anything. So I can make the board as I planned with the square header pins, and then use 2 strips of the female headers as adapters. It won't be pretty, or robust, but it might keep me going until I get the right ones.

[PCB.Wiz]

To fit into IC sockets you want round machined pin headers that are 0.018 inch (0.46 mm) on one side.

Thanks, I'll have to find some of those. For now I think I've figured out a way I can make it work: the female headers do fit in the socket. It doesn't feel perfect but I think it'll work without damaging anything. So I can make the board as I planned with the square header pins, and then use 2 strips of the female headers as adapters. It won't be pretty, or robust, but it might keep me going until I get the right ones.

If you have a pin-size issue, we used to use a standard DIP socket as an adaptor.
Even std square header pins can be 'forced into' a dual wipe DIP socket, but you do not really want to be doing that to your board-socket, so just use a 'sacrificial DIP socket', which are cheap and plentiful.

[bson]

Thanks, I'll have to find some of those.

One of the few items I actually buy on ebay...

https://www.ebay.com/itm/5-x-Gold-Plated-2-54mm-Male-40-Pin-Single-Row-Straight-Round-Pin-Header-Strips/254531586532

[johnkenyon]

To fit into IC sockets you want round machined pin headers that are 0.018 inch (0.46 mm) on one side.

Thanks, I'll have to find some of those. For now I think I've figured out a way I can make it work: the female headers do fit in the socket. It doesn't feel perfect but I think it'll work without damaging anything. So I can make the board as I planned with the square header pins, and then use 2 strips of the female headers as adapters. It won't be pretty, or robust, but it might keep me going until I get the right ones.

Where I come from we use the term "turned pin" instead of "machined pin" - this may make your search a little easier, however...

If I were going to fit a 2864 into a 2732 socket, I would do the following:
On a piece of paper, see how the pinout of pins 2 through 26 of the 2864 compare with pins 1-24 of the 2732A.
From the 2864 data sheet I'm looking at, the only difference is that pin 26 on the 2864 is "NC" and pin 24 of the 2732A is Vcc.

Now given the general desire to be able to plug multiple devices into the same PCB socket, it's pretty safe to say that the NC pin, aka "No connect", on the 2864 is capable of being connected to +5v without damaging the device.

So we can physically plug the "bottom" 24 pins of a 2864 into a 2732 socket, without ill effect, if we do something about the 4 pins "hanging off the top".

Pin 1 is an output (RDY/nBUSY) - we can ignore that
Pin 2 is A12 - we need to tie this high or low because we don't "need" it
Pin 27 is nWE. We don't want to write to the device, so this will be tied high (the "n" in nWE, or the bar over WE on the data sheet says "active low")
Pin 28 is Vcc, this needs to be tied to the Vcc on the socket.

Because we are lazy, the easiest approach is to tie pins 2, 28, 27 together and connect them to pin 26.
This gives us a 2864 device, which if programmed with data in 0x1000-0x0FFF will look like a 4kX8 ROM when inserted into a 2732A socket.

Practically the the exercise becomes:
1) Create a new 8k device image
Rather than get the manual out and figure out how to program the upper 4k of an 8k device, we create an double image, and assuming we saved a plain binary image:
Linux: cat original4k.rom original4k.rom > new8k.rom
DOS/Windows command prompt window: COPY /B original4k.rom + original4k.rom new8k.rom

2) Program the device

3) Bastardize the device
With a pair of pliers, carefully bend pins 1, 2, 27, 28 so that they go up and over the top of the body of the device.
Keep the pins as close to the device body as possible to avoid fouling any other device on the PCB
If you want, insulate pin 1.
Solder a wire to the top of pin 26 - the wide bit which doesn't go into the socket.
Route that wire over pins 27, 28 and pin 2, and tack it to the pin with solder.

By "wire" I mean a single strand of copper or tinned copper wire - I would probably strip a length of stranded hookup wire, pull out a single strand, and use that

4) Insert the modified 2864 into the PCB.
If there's a decoupling capacitor in the way, either bend it over (don't crack any ceramic capacitor), or replace it with a lower profile device
Consider putting the 2864 into a 24 pin socket to create headroom (use a standard socket unless the PCB socket is distorted, and never use gold plated stuff).

You could use a 2764 using a similar bodge:
Pin 1 is usually Vpp - check the data sheet to find out whether this should be tied to +5v, 0v or left floating.
Pin 27 is usually nPGM -

To be honest, a 2x64 to 2732 "bodge" is a lot easier than a masked ROM to EPROM conversion (See http://www.adsb.co.uk/bbc/adaptor.html - shoehorning a 32 pin 27C1001 into a 28pin masked ROM socket).

[injb]

To fit into IC sockets you want round machined pin headers that are 0.018 inch (0.46 mm) on one side.

Thanks, I'll have to find some of those. For now I think I've figured out a way I can make it work: the female headers do fit in the socket. It doesn't feel perfect but I think it'll work without damaging anything. So I can make the board as I planned with the square header pins, and then use 2 strips of the female headers as adapters. It won't be pretty, or robust, but it might keep me going until I get the right ones.

Where I come from we use the term "turned pin" instead of "machined pin" - this may make your search a little easier, however...

If I were going to fit a 2864 into a 2732 socket, I would do the following:
On a piece of paper, see how the pinout of pins 2 through 26 of the 2864 compare with pins 1-24 of the 2732A.
From the 2864 data sheet I'm looking at, the only difference is that pin 26 on the 2864 is "NC" and pin 24 of the 2732A is Vcc.

Now given the general desire to be able to plug multiple devices into the same PCB socket, it's pretty safe to say that the NC pin, aka "No connect", on the 2864 is capable of being connected to +5v without damaging the device.

So we can physically plug the "bottom" 24 pins of a 2864 into a 2732 socket, without ill effect, if we do something about the 4 pins "hanging off the top".

Pin 1 is an output (RDY/nBUSY) - we can ignore that
Pin 2 is A12 - we need to tie this high or low because we don't "need" it
Pin 27 is nWE. We don't want to write to the device, so this will be tied high (the "n" in nWE, or the bar over WE on the data sheet says "active low")
Pin 28 is Vcc, this needs to be tied to the Vcc on the socket.

Because we are lazy, the easiest approach is to tie pins 2, 28, 27 together and connect them to pin 26.
This gives us a 2864 device, which if programmed with data in 0x1000-0x0FFF will look like a 4kX8 ROM when inserted into a 2732A socket.

Practically the the exercise becomes:
1) Create a new 8k device image
Rather than get the manual out and figure out how to program the upper 4k of an 8k device, we create an double image, and assuming we saved a plain binary image:
Linux: cat original4k.rom original4k.rom > new8k.rom
DOS/Windows command prompt window: COPY /B original4k.rom + original4k.rom new8k.rom

2) Program the device

3) Bastardize the device
With a pair of pliers, carefully bend pins 1, 2, 27, 28 so that they go up and over the top of the body of the device.
Keep the pins as close to the device body as possible to avoid fouling any other device on the PCB
If you want, insulate pin 1.
Solder a wire to the top of pin 26 - the wide bit which doesn't go into the socket.
Route that wire over pins 27, 28 and pin 2, and tack it to the pin with solder.

By "wire" I mean a single strand of copper or tinned copper wire - I would probably strip a length of stranded hookup wire, pull out a single strand, and use that

4) Insert the modified 2864 into the PCB.
If there's a decoupling capacitor in the way, either bend it over (don't crack any ceramic capacitor), or replace it with a lower profile device
Consider putting the 2864 into a 24 pin socket to create headroom (use a standard socket unless the PCB socket is distorted, and never use gold plated stuff).

You could use a 2764 using a similar bodge:
Pin 1 is usually Vpp - check the data sheet to find out whether this should be tied to +5v, 0v or left floating.
Pin 27 is usually nPGM -

To be honest, a 2x64 to 2732 "bodge" is a lot easier than a masked ROM to EPROM conversion (See http://www.adsb.co.uk/bbc/adaptor.html - shoehorning a 32 pin 27C1001 into a 28pin masked ROM socket).

Thanks for the tips. I thought about soldering the pins directly but I ended up making an adapter with stripboard:



For the IC socket, I went to my local Fry's (incredibly they're still around) and got a 40 pin socket, which is probably literally the last item of any kind they had in stock

I had to cut out the supports to make room for my header pins. Infuriatingly, the header pins fit flush along the outside of the IC socket, but not the inside. If you look closely, there's more plastic on the inside than the outside. So the right thing to do is probably to put the header pins 2 spaces over instead of 1. But I discovered this after soldering the first set of header pins, so I had to sand the inner wall of the socket down to get my headers to sit straight.

Then to adapt the square pins (which were all I had on hand) to fit the target IC socket on the board, I just slipped on a strip of the female headers:



It's far from perfect but it works nicely.

For the next version I'll get the proper round pins, maybe a zif socket, and a switch that lets me choose between 2 images. For now I just doubled up the image using cat (exactly as described above).

Of course by the time I had all this done, my 2732As arrived from China anyway. But I'm glad I did this because it's much handier to reprogram.

[injb]

So, something strange happened while I was playing around with my new eeprom adapter. It stopped working after I removed and reattached the eeprom. Naturally I assumed I just wasn't making a good connection somewhere any longer, so I double checked everything. No amount of removing and reinstalling the adapter or the eeprom made any difference.

So I popped the eeprom into my programmer and tried reading it. It read just fine. Then I put the original UV eprom back in the board - that worked. Next I programmed a second eeprom with the same image, and put that in the adapter, and put the adapter in the board - that worked fine. I put the first one back - it would not work. So finally I programmed the first eeprom again with the same image, and it started working again!

So what's the story - can you somehow damage the image by handling so that you have to reprogram the chip? I never heard of anything like this before. But there's no mistaking it - it absolutely would not work until I reprogrammed it with the same image it already had. Any ideas?