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First post, by zuldan

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I would like to boot from an EPROM via a network card (using XTIDE rom https://www.xtideuniversalbios.org/). All the boot rom sockets on all my network cards have have 28 pins.

1. How do I know which EPROM is compatible on which card? Can I just buy any 28 EPROM? I was going to grab this one https://www.ebay.com.au/itm/304988470199

2. Why do they need to be erased with UV light? Can’t I just write zero’s to the EPROM with a programmer?

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Reply 1 of 9, by texspex

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zuldan wrote on 2023-12-11, 09:55:

1. How do I know which EPROM is compatible on which card? Can I just buy any 28 EPROM? I was going to grab this one https://www.ebay.com.au/itm/304988470199

2. Why do they need to be erased with UV light? Can’t I just write zero’s to the EPROM with a programmer?

1. Most NICs with a 28-pin ROM socket will follow a standard pinout. The manual for the NIC should contain information on what kind of EPROMs it supports, but I'm assuming you don't have the manual for it so it's trial and error then.
http://www.seeit.fr/uploads/docu/M27C128A.pdf
Here's a datasheet for the M27C128A which has the same pinout as if you'd google "27c128 pinout".
There are EPROMs with different pinouts, but it's unlikely you would need any of those.

2. I would assume the seller has UV erased the chip already (might wanna confirm that with the seller). So all you would need to do it program the XT-IDE BIOS .bin file to it. A blank EPROM is filled with 1's in every bit (hex FF). You can only program 1's into 0's on EPROMs. If there's any data on it it will contain 0's and it cannot be programmed into a 1. Then you would need to UV erase it to all 1's.

Reply 2 of 9, by zuldan

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texspex wrote on 2023-12-11, 11:24:
1. Most NICs with a 28-pin ROM socket will follow a standard pinout. The manual for the NIC should contain information on what k […]
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zuldan wrote on 2023-12-11, 09:55:

1. How do I know which EPROM is compatible on which card? Can I just buy any 28 EPROM? I was going to grab this one https://www.ebay.com.au/itm/304988470199

2. Why do they need to be erased with UV light? Can’t I just write zero’s to the EPROM with a programmer?

1. Most NICs with a 28-pin ROM socket will follow a standard pinout. The manual for the NIC should contain information on what kind of EPROMs it supports, but I'm assuming you don't have the manual for it so it's trial and error then.
http://www.seeit.fr/uploads/docu/M27C128A.pdf
Here's a datasheet for the M27C128A which has the same pinout as if you'd google "27c128 pinout".
There are EPROMs with different pinouts, but it's unlikely you would need any of those.

2. I would assume the seller has UV erased the chip already (might wanna confirm that with the seller). So all you would need to do it program the XT-IDE BIOS .bin file to it. A blank EPROM is filled with 1's in every bit (hex FF). You can only program 1's into 0's on EPROMs. If there's any data on it it will contain 0's and it cannot be programmed into a 1. Then you would need to UV erase it to all 1's.

Thank you so much for the explanation. Is there any reason why I couldn’t just leave the chip in the sun for 5 minutes to erase?

Reply 3 of 9, by texspex

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zuldan wrote on 2023-12-11, 11:33:

Thank you so much for the explanation. Is there any reason why I couldn’t just leave the chip in the sun for 5 minutes to erase?

The sun can erase it for sure, but usually it takes several hours to erase it completely in direct sunlight.
I'm not 100% sure, but if I remember correctly it has to do with the wavelength of the UV light. The needed wavelength is harmful to humans, but we can be in the sunlight quite safely. So the atmosphere doesn't let through so much of the harmful wavelengths.

Reply 4 of 9, by Yrouel

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Since you need to buy something buy an EEPROM instead, like a AT28C64B, so you won't have to worry about erasing it with UV in case you need to change something.

Remember you need to run the XT-IDE configuration first on the machine and save the binary and flash that one not what you download which lacks the checksum.

Also might need to properly configure the network card itself to set the size of the option rom you use (it might just work as is though)

Reply 5 of 9, by zuldan

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texspex wrote on 2023-12-11, 11:43:
zuldan wrote on 2023-12-11, 11:33:

Thank you so much for the explanation. Is there any reason why I couldn’t just leave the chip in the sun for 5 minutes to erase?

The sun can erase it for sure, but usually it takes several hours to erase it completely in direct sunlight.
I'm not 100% sure, but if I remember correctly it has to do with the wavelength of the UV light. The needed wavelength is harmful to humans, but we can be in the sunlight quite safely. So the atmosphere doesn't let through so much of the harmful wavelengths.

Ok sounds like you need a proper UV light to use these.

Reply 6 of 9, by zuldan

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Yrouel wrote on 2023-12-11, 11:43:

Since you need to buy something buy an EEPROM instead, like a AT28C64B, so you won't have to worry about erasing it with UV in case you need to change something.

Remember you need to run the XT-IDE configuration first on the machine and save the binary and flash that one not what you download which lacks the checksum.

Also might need to properly configure the network card itself to set the size of the option rom you use (it might just work as is though)

Do you think this one would be ok? https://www.ebay.com.au/itm/196105569736

And thanks for the tip!

Reply 7 of 9, by Yrouel

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zuldan wrote on 2023-12-11, 11:52:

Do you think this one would be ok? https://www.ebay.com.au/itm/196105569736

No that's OTP or One Time Programmable so you'd have a single shot and if you mess something you'd have to throw it away (it's essentially a UV EPROM in a plastic package and without a window it's not erasable).

You need something like a AT28C256 or the Winbond 27C512 (plastic black package), you want a 28 pin dip parallel EEPROM

Reply 8 of 9, by zuldan

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Yrouel wrote on 2023-12-11, 12:03:
zuldan wrote on 2023-12-11, 11:52:

Do you think this one would be ok? https://www.ebay.com.au/itm/196105569736

No that's OTP or One Time Programmable so you'd have a single shot and if you mess something you'd have to throw it away (it's essentially a UV EPROM in a plastic package and without a window it's not erasable).

You need something like a AT28C256 or the Winbond 27C512 (plastic black package), you want a 28 pin dip parallel EEPROM

Ok interesting. Learning a lot here 😀

How about this one? https://au.element14.com/microchip/at28c64b-1 … -x-8/dp/1095784