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DALLAS DS1687 suddenly has password set

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First post, by majestyk

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From time to time I order a bunch of original DS1687-5+ or similar from Digikey or Mouser. They´re not just a bargain but the optical impression is very close to the original RTCs (except for the "recycle bin").

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Last week I put one of them in a FIC 4386-VC-HD, entered all the settings and everything worked fine.
Yesterday when I wanted to enter the BIOS menue I was asked for a password that I never set.
I tried all the default passwords - no luck.

This RTC has a reset pin that can be used to clear all the user data. It must be connected to "VBatt" so I dremeled a bit to get hold of this pin that´s not reachable from the outside.

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After shorting the pins, it would still ask for the password. Then I found this note in the manual:

The attachment dallas_pwd.JPG is no longer available

Are they serious?
Assuming the memory for the password was volatile I went for the second battery pin - just as you do to mod old Dallas RTCs - and shorted both pins for about two seconds.
After that the password had been reset.

The attachment dallas_3.JPG is no longer available

Reply 1 of 6, by kitten.may.cry

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That's messed up, yo!

Reply 2 of 6, by chrismeyer6

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Wow that's one weird issue with that Dallas chip. I'm glad you got it all sorted out. I'm really curious as to what caused it to think you set a password on it.

Reply 3 of 6, by Horun

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Thanks for the info ! I have never seen a board that came with a 1687, have many with 1287/12887 and two with 1587's. Very interesting...
Based on your findings I will not be using any to replace the 1287 or 12887's since you cannot clear the password. Have never had a problem with the 12887's even non-A versions...
Your clip of the manual does not match any I have for 12887, can you link that exact manual ?

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 4 of 6, by Sphere478

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There ya go. good job. Shorting the battery should definitely clear it 🤣.

Personally, I like replacing these with aftermarket units that can use a coin cell. monotech has one that can use a full size battery.

Sphere's PCB projects.
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Sphere’s socket 5/7 cpu collection.
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SUCCESSFUL K6-2+ to K6-3+ Full Cache Enable Mod
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Tyan S1564S to S1564D single to dual processor conversion (also s1563 and s1562)

Reply 5 of 6, by majestyk

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Horun wrote on 2022-06-01, 23:46:

Thanks for the info ! I have never seen a board that came with a 1687, have many with 1287/12887 and two with 1587's. Very interesting...
Based on your findings I will not be using any to replace the 1287 or 12887's since you cannot clear the password. Have never had a problem with the 12887's even non-A versions...
Your clip of the manual does not match any I have for 12887, can you link that exact manual ?

I just checked back and found this is not some original DALLAS / MAXIM manual, but a document I downloaded years ago and saved under my "DALLAS"-folder.
https://ardent-tool.com/misc/DalSemiRTCModuleFAQ.pdf

I cannot tell what´s true here, I generally don´t set BIOS passwords and rarely had to reset passwords let alone on systems with DALLAS RTCs. Today they all have dead batteries anyway so old passwords would be reset.
The reason for ordering DS1687s was availability. These are all datecode 2020 while when you´re buying from some Ebay seller in China the printings on the chips mean nothing.
AFAIK the "5" means it´s for 5 Volt, the plus means an extended temperature range (which doesn´t hurt). The 1687 models also have aunique 64bit serial number stored in memory. Maybe that´s why a certain memory range cannot be reset?

Reply 6 of 6, by Horun

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Thanks ! The 1585/1587 also has a 64 serial, maybe these 1687 are designed to replace both 1287 and 1587 ??? My Dual Pentium board uses a 1587 and a 1287 does not work in it.
Maybe I will buy a couple 😀

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

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