DS1386 RAMified Watchdog Timekeeper

adrianhudson · Post by **adrianhudson** » Sat Aug 06, 2022 9:49 am

I came acrosss this chip. What a curious animal. Its like a 62256 - with almost identical pinout but with 4 extra pins stuck on the end - but NV RAM and with an inbuilt clock. The clock uses the first 14 bytes of memory.

I cant decide whether it could replace a 32K EEPROM or the 32K RAM in my SBC. I suspect it is a bit slow (although I only run the 02 at 1mHz.

Has anyone ever used one of these?

BigEd · Post by **BigEd** » Sat Aug 06, 2022 10:44 am

Haven't but it does seem like an interesting offering!

It's also obsolete so the question becomes: can you find one? (If it happens to be a part with a built in battery then very old stock might be no use to you. Edit: "The DS1386 contains a lithium energy source and a quartz crystal")

I found some similar products, in stock, prices from £22 upwards so not cheap:
https://www.mouser.co.uk/c/semiconducto ... ory%20Size

adrianhudson · Post by **adrianhudson** » Sat Aug 06, 2022 2:41 pm

Yes, I saw those on mouser. I like the 'Y2K compliant' bit. That shows their age!

I'm tempted by a Chinese 'new' one at £3.50 on ebay but as you say, the battery is probably knack*d. Still at £3.50, it might give me an afternoon's 'fun'.

BigEd · Post by **BigEd** » Sat Aug 06, 2022 2:46 pm

I've seen people show how you can take a dremel to some of these packages, to expose the internal supply rail and to allow the fitting of an external battery. Of course you'd need to have the right part in the right package to be sure of excavating the right spot.

BillO · Post by **BillO** » Sat Aug 06, 2022 2:59 pm

I have some DS1225 NV RAM and they were working fine up until s couple of years ago when I last used them. If they are NOS and have never been powered up the battery might be OK. I think they may not activate the battery until the first power up then loss. That's only a theory though, other wise they would have awful shelf life.

adrianhudson · Post by **adrianhudson** » Sat Aug 06, 2022 4:08 pm

BigEd: blimey, that would be fairly tricky!

BillO. The datasheet says they are shipped from factory with a bit set so the oscillator is stopped. But 50/50 chance a Chinese 'new' one won't be (new) I would guess.

Dr Jefyll · Post by **Dr Jefyll** » Sat Aug 06, 2022 4:42 pm

adrianhudson wrote:

BigEd: blimey, that would be fairly tricky!

It might give you an afternoon's 'fun', Adrian!

Proxy · Post by **Proxy** » Sat Aug 06, 2022 4:47 pm

BigEd wrote:

I've seen people show how you can take a dremel to some of these packages, to expose the internal supply rail and to allow the fitting of an external battery. Of course you'd need to have the right part in the right package to be sure of excavating the right spot.

I once did that for an old 386 PC using nothing but a triangle file and vice, it was surprisingly easy.
I put a generic CR2032 cell holder ontop and it works perfectly fine.

EDIT: i still have one of those but without the holes, a DS1287 to be exact

adrianhudson · Post by **adrianhudson** » Sat Aug 06, 2022 5:52 pm

Me <- impressed

Guus Assmann · Post by **Guus Assmann** » Wed Aug 10, 2022 6:21 pm

Been there, done that.
I mean both replacing the battery by opening up the top.
And also using it instead of a "normal" ram.

They mostly are 150nS, but can be had with 120nS and even 85nS.
And if really new, the battery is switched off until the first power up.

To use them as a Ram replacement, make sure the first 14 bytes are not used.
And there's also other devices, that have the clock at the end of the memory, the last 14 bytes.

BR/
Guus

BigEd · Post by **BigEd** » Mon Aug 22, 2022 6:42 pm

BigEd wrote:

I found some similar products, in stock, prices from £22 upwards so not cheap:
https://www.mouser.co.uk/c/semiconducto ... ory%20Size

It turns out there are other non-volatile SRAM offerings, including FRAMs, which I think we've mentioned previously, with some possible concern about limited write cycles. A search at digikey for nvsram or fram, in through hole, 5V supply, parallel interface, turns up 79 in-stock products starting at £9. That's for an 8kByte part. For a 32kByte part, starting at £11. This link might work.