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Modern alternative for UV EPROMs

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Rauli

Experienced Member
Joined
Sep 16, 2013
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114
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Spain
Hi. I would like to write a ROM BIOS extension for an old PC.

The idea is to burn an EEPROM with a programmer, and to use the chip in a network ISA card. The PC will not be on any network, but it is an ISA card which I can plug in the PC and the card has a socket for a PROM.

The card is a 3Com 3c509b, and the manual mentions that 8, 16 and 32 Kb EPROMs can be used, but does not specify which chip models. The socket is a DIP 28, so I suppose it refers to 27c64, 27c128 and 27c256 chips.

I suppose UV EPROMs can be acquired some way, but I have not an UV eraser, and I don't want to buy or make one, because it is a very slow method and I will need to make many erase/burn tries.

I have taken a look at the 27cxx (UV EPROM) chips datasheets and compared to the 28cxx (EEPROM) and 29cxx (flash) ones. The 29cxx turned out to have the most similar pinout, with only pin 1 different. This is the write enable pin, which is active high for the 27cxx and active low for the 29cxx. Also, it needs a higher voltage on the old 27cxx.

On the 28cxx the write enable pin levels are the same as in the 29cxx, but in addition it swaps pins 1 and 27.

So I suppose the best replacement for a 27cxx is a 29cxx, probably leaving pin 1 unconnected.

Has anybody tried this, or found a different alternative?

Note: To program the 28cxx or 29cxx I can use a modern programmer, so when I say "alternative" or "replacement" I mean for read-only operation (the network card will just read the chip, it will not try to program it).
 
Both 28Cxxx and 29Cxxx can be programmed in system, given a card with correct pin out, including /MEMW signal. Some cards designed by people here will do that. XT-IDE, my XT-CF-Lite version, and FDC and serial card support programming of 28Cxxx. XT-CF and follow up cards designed by James support 29Fxxx.
29Fxxxx have pinout more similar to 27xxx, and 28Cxxx have pinout more similar to that of SRAM ICs.
 
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I just recently converted the monitor program in my 8080A computer from 2716 EPROM to 28C16 EEPROM. I have a board in the machine that has 16 sockets for 2K memory chips. On one of the sockets I added a jumper post with three pins. The center pin goes to the EEPROM Pin 20. The outside pins go to MEMW and ground. The ground being the normal jumper connection. When I want to change the programming of a chip in this spot, I have to move the jumper to the MEMW position and then I can easily program it. If I only have to change a hand full of spots, I can do it from the front panel switches. If a significant fraction or all of it needs programming I write a short routine to do it. You need to have the data and MEMW present for each data spot for 10 ms. It's not hard and it works great. Mike
 
Thanks, but maybe my question was not clear.

I have no problem in programming EEPROMs or flash chips.

I just would like to know which alternative can be used to replace 27cxxx chips found in many vintage hardware, not just in the network card I'm using for this project.

And I'm looking for "read-only" compatibility, as boards and cards using the 27cxxx UV EPROMs just read the chip, never write it.
 
Rauli said:
Thanks, but maybe my question was not clear.

I have no problem in programming EEPROMs or flash chips.

I just would like to know which alternative can be used to replace 27cxxx chips found in many vintage hardware, not just in the network card I'm using for this project.

And I'm looking for "read-only" compatibility, as boards and cards using the 27cxxx UV EPROMs just read the chip, never write it.
Click to expand...

You answered your question yourself - use 29Fxxx/39SFxxx Flash ROMs or 28Cxxx EEPROMs. Currently it looks that Microchip SST39SF010A/SST39SF020A/SST39SF040 is the best option (cheap, fast, and still in production). If your project is using smaller than 128 KiB ROM, you still can use one of these ICs, just program the code into lower addresses and connect unused address lines to GND. If you want a "Read-Only" functionality, you can tie /WR input to VCC.
 
Rauli said:
Thanks, but maybe my question was not clear.

I have no problem in programming EEPROMs or flash chips.

I just would like to know which alternative can be used to replace 27cxxx chips found in many vintage hardware, not just in the network card I'm using for this project.

And I'm looking for "read-only" compatibility, as boards and cards using the 27cxxx UV EPROMs just read the chip, never write it.
Click to expand...
I use Atmel 29C256 chips in my IBM 5155 portable and they work great. I can make changes to the bios without getting out the UV eraser. I use an "adapter" under the chip which consists of a modified Zif Socket plugged into the Motherboard socket. I clipped off pin 1 on the bottom side then removed the top and soldered a small wire between pin 1 and pin 28 to supply +5v to WE to protect the contents of the eeprom. Then, with some minor modification to the plastic to make room for the jumper wire and solder, I put the tops back on and plugged them into the Mother board, inserted the programmed 29c256's and booted it up. The Zif sockets with the eeproms plugged in stand pretty tall, but they make removing and installing the chips so much easier.
 
So the idea is to use 29cxxx chips with pin 1 not unconnected, but connected to pin 28. And to use an intermediate socket to make that connection and to help insertion/removal of the chip. Thanks.
 
The Winbond W27E257 has the same pinout as a 27C256. Pin 1 is VPP and should be equal to VCC, except when raised to the erase (14V) or program (12V) voltages.

You can try your luck buying 10 of them including shipping from HK / China for around $15 on eBay.
 
Another idea... my intel etherlink 16 natively uses a flash part (dont remember which one). it came from the factory this way! can flash in system, or remove chip from socket and use a regular programmer.
 
gslick said:
The Winbond W27E257 has the same pinout as a 27C256. Pin 1 is VPP and should be equal to VCC, except when raised to the erase (14V) or program (12V) voltages.
Click to expand...

Thanks. I didn't know this one, but it seems almost identical to the original 27cxxx series. For read-only environments it doesn't need any jumper or adapter, I have to check if my programmer supports it.
 
I am replying to an old thread. @Rauli - did you complete your project? I too have a project where I want to use something electrically erasable in place of the 27C64. If you found the Winbond to work I would love to hear about it.
 
w2hx said:
I am replying to an old thread. @Rauli - did you complete your project? I too have a project where I want to use something electrically erasable in place of the 27C64. If you found the Winbond to work I would love to hear about it.
Click to expand...

Found a good deal on Ebay for some Winbond W27E257-12 chips, so, I bought them. My programmer appears to support them, so I'll let you know how they work. They should work in place of the 27c64 but only the top 1/4 would be readable in the circuit designed for the 64 kbit chip.

Greg
 
ibmapc said:
Found a good deal on Ebay for some Winbond W27E257-12 chips, so, I bought them. My programmer appears to support them, so I'll let you know how they work. They should work in place of the 27c64 but only the top 1/4 would be readable in the circuit designed for the 64 kbit chip.

Greg
Click to expand...

Hi. Sorry if I'm asking before you've had a chance to try but just wondering if you had any success with using the Winbond W27E257-12 chips as drop-in read-only replacements for your 27cxxx EPROMS? I'm trying to revive an old IBM XT clone and the original 2764 EPROM seems to need replacing - so I'm curious if the Winbond W27E257-12 chips are an option.
 
EleDip said:
Hi. Sorry if I'm asking before you've had a chance to try but just wondering if you had any success with using the Winbond W27E257-12 chips as drop-in read-only replacements for your 27cxxx EPROMS? I'm trying to revive an old IBM XT clone and the original 2764 EPROM seems to need replacing - so I'm curious if the Winbond W27E257-12 chips are an option.
Click to expand...

If you're not planning on reprogramming the ROMs multiple times, you can use the OTP version of the 27C256. It is still being made, and it is dirt cheap. When replacing a 2764 just mirror the ROM image 4 times, so it is accessible regardless of the connection of pins 26 and 27.
 
ibmapc said:
Found a good deal on Ebay for some Winbond W27E257-12 chips, so, I bought them. My programmer appears to support them, so I'll let you know how they work. They should work in place of the 27c64 but only the top 1/4 would be readable in the circuit designed for the 64 kbit chip.
Greg
Click to expand...
EleDip said:
Hi. Sorry if I'm asking before you've had a chance to try but just wondering if you had any success with using the Winbond W27E257-12 chips as drop-in read-only replacements for your 27cxxx EPROMS?
Click to expand...
I have lots of 27C256, which is what I use in the IBM PC (with adapter), IBM XT, and IBM AT.
Although erasing UV type EPROM's is not much of a hassle for me, I decided to try the W27E257 as a replacement for 27C256.
Some W27E257-12's arrived on Friday.
They work in my IBM PC (via adapter), early IBM XT, later IBM XT, and IBM AT.

The fact that they work in the early XT was a relief. I have now included the W27E257 in the 'Early 5160 motherboards' section at [here].
 
Krille said:
I guess another alternative might be the SST27SF256 flash ROMs. Very cheap on ebay.
Click to expand...

I bought 10 of these from this listing because the data sheet says that they are drop-in replacements for 27Cxxx ROMs so my plan was to use them to host XTIDE Universal BIOS on NICs with ROM sockets. The package arrived some time ago and even though the listing claims that the ROMs are new they were kind of dirty and had scratches plus a lot of bent pins. So obviously not new. No biggie though, I figured - I have a pair of needle-nose pliers and lots of patience.

Then I tried them in my programmer (a MiniPro TL866A) and the software reports that the selected chip doesn't match the ChipID read from the ROMs (the ID is DA 02 and I can't find out what type of ROM that is supposed to be). After a bit of googling I found this site and it turns out they are all fake. I requested and got a refund from the seller but the listing is still up so he doesn't seem to be overly concerned about selling useless counterfeits. When looking at his feedback I see many people complaining about fake items so I guess the joke is on me for not checking the feedback before buying.

Anyway, I figured I should give you all a heads-up so no one else wastes time and money on this crap.
 
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