VOGONS


First post, by Jonas-fr

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I recently stumbled upon a nice 486 lugable akin to a Dolch (dedicated topic is yet to come) with a battery dead ST MK48T87B RTC (DS1287 pin compatible if I'm not mistaken). As the whole machine since to be build to be maintainable (not mil spec but pretty close) it's socketed so I intend to replace it.

I looked around and I have the following options :
- buy a compatible RTC replacement and hack it to support an external battery > I'm comfortable with that since I've got the tools and the steady hands to do it
- get a nice GW-1287 from tindie (what a cool project really) > this would be perfect but as I'm located in Europe the shipping cost is killing the deal (about 2 times the price of the item)

Seeing that the GW board shouldn't be too complicated I'm wondering whether an open source hardware replacement exists in order to let anyone with a soldering iron to do its own replacements chips. Don't get me wrong I'd glasdly support the maker of this wonderful project, but I'd rather see my money in his pocket than in the US postal system that rips people off for international shipping.

Reply 1 of 14, by matze79

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ALT12887

https://dosreloaded.de - The German Retro DOS PC Community
https://www.retroianer.de - under constructing since ever

Co2 - for a endless Summer

Reply 2 of 14, by appiah4

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Are the DS12885 chips used on the ALT12887 boards cheap and easy to source?

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 3 of 14, by Jonas-fr

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matze79 wrote on 2020-07-07, 10:08:

ALT12887

Thanks ! I was not aware of that project, I will check this out. Just a quick question, the datasheet of my chip says that it's DS1287 compatible (cf. page 2 on https://www.datasheets360.com/pdf/7995962487213876287), what's the difference with a DS12887? I think they're pin compatible and the latter is just Y2K compliant is that so?

EDIT: well I just found what I need with related links on the ALT12887 project: https://oshpark.com/shared_projects/EfNaK3A6

Reply 4 of 14, by appiah4

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Jonas-fr wrote on 2020-07-07, 10:34:
matze79 wrote on 2020-07-07, 10:08:

ALT12887

Thanks ! I was not aware of that project, I will check this out. Just a quick question, the datasheet of my chip says that it's DS1287 compatible (cf. page 2 on https://www.datasheets360.com/pdf/7995962487213876287), what's the difference with a DS12887? I think they're pin compatible and the latter is just Y2K compliant is that so?

EDIT: well I just found what I need with related links on the ALT12887 project: https://oshpark.com/shared_projects/EfNaK3A6

Yes but I have seen boards that worked with a DS1287 and not boot with a DS12C887 for example so I am not sure 1287/12887/12C887/12C887+ are 100% compatible with each other as they are supposed to be..

EDIT: What IC does this version use? SMH

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 5 of 14, by Jonas-fr

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Yeah the C variants have many quirks it seems. I just located a clear DS12887 datasheet that states that 12887 is a direct replacement for a DS1287 and just add some more RAM so it would mean that I can go with the ALT12887 project. Thanks for your feedback !

Reply 7 of 14, by my03

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Are you in the Nordics? Tme should supposedly get a batch of 12887+ now in July. I did not want to wait (in April) so i bought mine from digikey

(Replaced the rtc in my ps/2 model 30-286)

Reply 8 of 14, by appiah4

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maxtherabbit wrote on 2020-07-07, 13:53:

Why not just buy a brand new DS12887+ from digikey?

At least for me shipping is a big cost item for getting supply from places like digikey and mouser. More local places tend to have rather old stock (5-10 years old). I would rather invest once in something like this and have a steady supply of easy to change coin batteries.

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 9 of 14, by matze79

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Jonas-fr wrote on 2020-07-07, 10:43:

Yeah the C variants have many quirks it seems. I just located a clear DS12887 datasheet that states that 12887 is a direct replacement for a DS1287 and just add some more RAM so it would mean that I can go with the ALT12887 project. Thanks for your feedback !

ALT12887 does not run in Intel Batman.
at least my P60 does not work with it.

In my 55SX PS/2 Modell its working fine.
Also on several Intel Socket 5/7 Mainboards its fine.

https://dosreloaded.de - The German Retro DOS PC Community
https://www.retroianer.de - under constructing since ever

Co2 - for a endless Summer

Reply 10 of 14, by my03

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appiah4 wrote on 2020-07-08, 07:22:
maxtherabbit wrote on 2020-07-07, 13:53:

Why not just buy a brand new DS12887+ from digikey?

At least for me shipping is a big cost item for getting supply from places like digikey and mouser. More local places tend to have rather old stock (5-10 years old). I would rather invest once in something like this and have a steady supply of easy to change coin batteries.

Idk really about the age of these, but i do know that Dallas is nowadays 'Maxim' and they still sell the 12887+ (and the distributors get refills) so perhaps not an investment on a 15+ year scale, but imho better than nothing.

(for example: https://www.tme.eu/se/en/details/ds12887+/rtc … xim-integrated/)

Reply 11 of 14, by Jonas-fr

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maxtherabbit wrote on 2020-07-07, 13:53:

Why not just buy a brand new DS12887+ from digikey?

Because I want to make the next maintenance to be easy and don't want to continue the ecologically-desastrous habit of throwing an otherwise good chip just because its battery is bad. If it was up to me I would ban such wasteful products from the market.

Reply 12 of 14, by appiah4

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I've looked into sourcing parts and building these myself as well but the DS12885 does not seem to be a cheap acquisition in the required SOIC packge type..

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 13 of 14, by Jonas-fr

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appiah4 wrote on 2020-07-10, 07:30:

I've looked into sourcing parts and building these myself as well but the DS12885 does not seem to be a cheap acquisition in the required SOIC packge type..

I see some at <$2 so still acceptable price IMO (but again the shipping cost are ruining all the deals)
http://www.utsource.net/sch/DS12885S.html