How to pick a bootrom

I've created lots of bootroms for various cards. It's one of those things that was a mystery to me until I actually sat down and learned how to do it. Now, it seems so easy

The chips you need depend entirely on the card. Start by looking at the socket.

If it is a 28-pin, then likely a 27c128 or 27c256 will do the trick for you. You'll also have to pick the speed of the chip. I try to stick with 150's or faster. The part number would usually be something like 27c128-150. The 27c128 and 27c256 chips seem to be really hard to find. I'm worried that at some point, they will dissappear from the market completely.

For the rtl8139 based cards that i've used, they either had a 28-pin or a 32-pin socket. In both cases, I could use the 27c128 chips. You just need to insert the 28-pin chip into the bottom end of the 32-pin socket. That is, the extra holes in the socket are at the end where the notch is. I've drawn a crude picture of a chip, it's at the bottom of this document.

For the 3c905 cards, they have a 32-pin DIPP socket. For those, I use a flash chip. The 3Com literature says that only an Atmel AT29C512 is supported. The full part number on that is AT29C512-12PC. But, I've used lots of SST Chips for the 3c905. The full part number on those is 29EE512-90-4C-PH. I've heard that the 27c256 will work in the 3c905, but i've never tried it.

The SST chip also works on the Linksys LNE100TX v4 and v5 cards.

There's also another type of socket. A small almost square chip that doesn't look anything like the 28 or 32-pin chips.

Those are called PLCC chips. Some of the Intel eepro100 have that kind of socket.

For bootrom programmers, I use (and recommend) the eprom programmer that we sell at DisklessWorkstations.Com I know that I am probably biased, because I am part owner of the company, but I really like that programming unit. I've made thousands of bootroms with it, for over 7 years, and it is a real workhorse. It will handle many different kinds of chips, including the PLCC's, with a special adapter. The only downside with this programmer is that the software only runs under DOS.

There are lots of other eprom programmers out there as well. Some in the neighborhood of $100, and others over $1000. Just make sure it supports the type of chip you need. I'd imagine they would all support the 27c128 eeprom, and they might support the flash '29' series chip.

One other thing to look for in a chip is whether it is a one-time programmable chip, or if it can be erased.

The 29 series chips are flash. They can be reprogrammed fairly easily. The 27 series come in either a plastic package or a ceramic package. You can tell the difference, because the ceramic package has a little glass window on the top that you can use to expose the chip to ultraviolet light, which will erase it.

The plastic chip is one-time programmable and the ceramic chip is eraseable.

Here's a crude picture of how to use a 28-pin chip in a 32-pin socket:

     +----------------------------+
    /                            /|               28-pin Chip
   /                           (  +
  /                            / /
 +----------------------------+ /
 |                            |/
 +----------------------------+
   | | | | | | | | | | | | | |

    +---------------------------------+
   / o o o o o o o o o o o o o o o o /|           32-pin socket
  /                                (  +
 / o o o o o o o o o o o o o o o o / /
+---------------------------------+ /
|                                 |/
+---------------------------------+

Notice the extra holes in the socket at the right hand side.

I hope this information is helpful,

Jim McQuillan jam@Ltsp.org