Bipolar PROM replacement?

But is the system running code from that 74S471? Sometimes those PROMs were used as glue logic, i.e. to implement a random logic function, like in a PAL or GAL. For that purpose, you need a faster device than for running code.

Finding chips or equivalents is always easier than re-engineering the device.

Hmmm... Pricy, but hardly scarce:

There's also a National 74LS471, which might work depending in output loading and stay cooler: Cheaper too. Also, think about stick on or clamp on DIP heat sinks.

For equivalent chips, see: Looks like the 74S471 can be replaced by a various devices. Be sure to compare spec sheets for differences.

This chip is in a Netronics ElfII, an 1802 based system from 79-80 era. It runs a monitor program in this chip (load to memory, save to cassette, etc.) I presume they used it as a cheaper alternative to the EPROMS of the day. I'm the original owner, and after starting it up back in 1980 or so, I noticed it was too hot (as in burning finger hot), so I attached a little chip heat-sink on it. I'm thinking now that that's what allowed to to last so many decades. I've read reports of these hot running PROMS in old video games that literally burn their pins off from heat accelerated corrosion.

As an aside, the monitor is only 256 bytes and addressed at F000 hex. I'm thinking if I use a 2732, I can claim the remaining address space to FFFF for other utilities in the 4K EPROM.

-J

Is there some reason you can't just plug in the 74LS471, assuming the pinout is the same as 74S471? Do you want me to check for you? I would prefer that you do this yourself (because I'm lazy today).

As I recall, the fastest 1802 clock was 4 to 5MHz. In about 1978, I had a product with a development system that ran at 3.58MHz and used Intel 2716 UV erasable EPROM's. I vaguely recall using someones 250 nsec RAM. The 2708, 2716, and 2732 were rather horrible in every way possible. However, things started to improve with the 2764 which could be found down to 120 nsec. Looks like your Elf II will take up to 16Kbits EPROM, and to 64Kbits with an expansion card. I don't know what kind of socket derrangement your Elf II has, but if it will accept a 24 or 28 pin DIP, it should work. The ELF II runs a

Anyway, that should be sufficient to get you started in what I hope is the right direction.

Incidentally, I should have a tube or two of 2764 EPROMs left over from the bad olde daze when I had to update mobile radios and PC motherboard BIOS's with a UV eraser and EPROM burner. Bug me via email if you can't find any and need some.

Thanks for the offer Jeff. But I have a few EPROMs laying about just waiting to be used. I noticed you referenced the Wikipedia entry on the Elf II. In fact, that is my Elf II in the photos!

I have a source for the 74S471 chips, but the problem is how to program them. They are 'fusible link' types and all three of my programmers won't handle them. And even if I found a way, it would still run hot. So that's why I'm thinking of a daughterboard that plugs into the original socket and holds a larger, slower, cooler EPROM chip.

And since I have the Netronics Full Basic ROM card, I know the machine can run code directly from 2716 chips (450ns). I even added a fourth

The 74LS471 you mentioned is a new possibility I hadn't considered. Lower power should reduce the heat a bit. I'll look into that too. If I can find a programmer for it, that would look more in 'spec' for the vintage machine.

Thanks!

-J

Ok in that case it should be possible to use an EPROM with a suitable adapter PCB to convert the 24pin .5" socket for a small EPROM to the

A lot. Look at the data sheets. (I'm still too lazy today).

Ummm... they're all over the web:

Since this is beginning to look like a one time use for the PROM burner, you might consider having someone with a bipolar PROM burner do the work. For example: Otherwise, a 2716/32/64 EPROM might be easier to program.

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Hi John,

I have a Data IO 29B with Unipack 2B that will program the 74LS471. Email me for details jrr@@@flippers...com (spam@@@flippers...com is also

valid - the 'bots don't believe it so I get little to no junk email on that address)

I am in Canada which may or may not be helpful for postage.

John :-#)#

Just in case someone might need a faster PROM replacement, here is an idea:

Yes it is running code in the PROM. That's the Monitor program for the computer.

-J