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| Jeff Liebermann <jeffl@cruzio.com>: Jul 04 10:19AM -0700 On Sat, 3 Jul 2021 19:44:12 -0500, John Crane >I know the PROMs run faster than the EPROM, but this is a vintage >computing project, and the machine runs code from a 2716 just fine. >-J Finding chips or equivalents is always easier than re-engineering the device. Hmmm... Pricy, but hardly scarce: <https://www.ebay.com/sch/i.html?_nkw=74s471> There's also a National 74LS471, which might work depending in output loading and stay cooler: <https://www.ebay.com/sch/i.html?_nkw=74ls471> Cheaper too. Also, think about stick on or clamp on DIP heat sinks. For equivalent chips, see: <https://www.mikesarcade.com/cgi-bin/spies.cgi?action=url&type=info&page=PromRef.txt> Looks like the 74S471 can be replaced by a various devices. Be sure to compare spec sheets for differences. -- Jeff Liebermann jeffl@cruzio.com PO Box 272 http://www.LearnByDestroying.com Ben Lomond CA 95005-0272 Skype: JeffLiebermann AE6KS 831-336-2558 |
| John Crane <john_crane_59@yahoo.com>: Jul 04 05:11PM -0500 On 7/4/21 12:19 PM, Jeff Liebermann wrote: 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 |
| Jeff Liebermann <jeffl@cruzio.com>: Jul 04 04:07PM -0700 On Sun, 4 Jul 2021 17:11:44 -0500, John Crane >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. <https://en.wikipedia.org/wiki/ELF_II> 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 1.76MHz clock, so you should be ok with most 27xx EPROM speeds. <http://www.cosmacvip.com/ELFII/ElfII.html> The above article mentions a 74C471 PROM, which might be another possibility. However, I couldn't find any other evidence that such a PROM existed. 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. -- Jeff Liebermann jeffl@cruzio.com PO Box 272 http://www.LearnByDestroying.com Ben Lomond CA 95005-0272 Skype: JeffLiebermann AE6KS 831-336-2558 |
| John Crane <john_crane_59@yahoo.com>: Jul 05 03:13AM -0500 On 7/4/21 6:07 PM, Jeff Liebermann wrote: > 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 2716 in the spare socket on the card to hold some utilities: serial loader, term i/o, the RCA SCRT routines, etc. And they all work just fine. 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 |
| Rob <nomail@example.com>: Jul 05 11:09AM +0200 > 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. 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 20pin .3" used by the PROM. |
| Jeroni Paul <JERONI.PAUL@terra.es>: Jul 04 04:39PM -0700 If it has a year setting it could it be out of range. You could set a past year to try. |
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