Dallas chips

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Re: Dallas chips

Unread postby Kumba » Sun Mar 26, 2017 8:03 pm

praetor242 wrote:I had ordered new Dallas chips for my nekkid O2, the only one is DS1687-5+, not the DS1687-5. When I put in the new chip, the O2 doesn't turn on. Where can I get the exact Dallas chip it needs?

A bit late to the convo. Any DS1687* chips you find these days are going to be old, and the battery would likely be questionable. The direct replacement part will be a Dallas/Maxim DS17x87 chip (the x is either 2, 4, or 8; all three will work), and it MUST be the 5V versions, so go with a part number like "DS17887-5+-ND" on websites like Digikey or Mouser. These are still currently made, so you're guaranteed to get a good battery in them. I have a DS17887 in my Octane and a DS17287 in my O2, and both work fine. I even wrote a Linux driver for these chips based off an early skeleton driver found on Google. You can look at drivers/rtc/rtc-ds1685.c if curious in a recent (4.x+) kernel tree.

On both O2 and Octane, this RTC chip provides the power signal, which is why when you replaced yours, it didn't want to power up initially. This means that specific DS1687-5 you had was either bad or messed up in unknown ways. I've found that you have to energize/de-energize the system a few times to get them to want to turn back on. I haven't worked out a specific sequence, but the NVRAM on these RTC's in Bank 0 holds several of the PROM variables, and I wonder if switching RTC's out doesn't scramble something temporarily or not. Plus, once it does power on, the PROM will reset the "TOD clock", and you'll want to power cycle it a final time to make sure it's fully descrambled itself.
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Re: Dallas chips

Unread postby japes » Mon Mar 27, 2017 4:17 pm

DS1687-5+ is an active part according to Maxim. Looks like the DS17x87-5 would work, but has a bunch more NV memory.
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