Electronics > Repair

Reverse engineer Dallas DS1742W?

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zebity:
Hi James_s and others,

happy to report that this nut has been cracked, not once but twice, by SGI community.

see this post on IRIX Network for drop in replacement by cz7asm with working clock and nvram:

https://forums.irixnet.org/thread-3360.html

And these post on SGI User Group:

By cz7asm: https://forums.sgi.sh/index.php?threads/ds1742-nvram-chip-replacement.702/

And Glitchworks prototype: https://forums.sgi.sh/index.php?threads/dallas-ds1742w-replacement.707/

I read the cuebus post, but it is not clear to me if this provides both RTC and NVRAM solution. If so then that gives three replacement options…

I have personally tested the cz7asm version, in SGI O350 (I am jwhat on IRIX Network) and confirmed it works like a charm. It has also been verified in SGI Fuel.

I have no affiliation with either cz7asm or Glitchworks, I am just another person who was doing drilling and investigation to see if a replacement solution could be found.

It would be good to know if the replacement options also worked in other equipment.

Cheers from Oz,

zebity (jwhat/John)


cz7asm:
Hi, if anyone is interested I have the DS1742W replacement available on ebay - https://www.ebay.com/itm/284766293220

Thank you zebity/John for spreading the word.

james_s:
Looks good. I'm curious, what IC did you base it on? Did you have to find a source of Dallas custom ICs or did you come up with a modern solution using current production parts?

zebity:
Hi James_s,

looking at it, it looks like it is DS1558D based,

So I presume to get this to behave the same as DS1742 you just have to hold the lower of the additional address lines (A0-A8 ?) high to make sure the RTC Clock addressing is mapped correctly.

As DS1742 has A0 - A10 and DS1558D has A0-A18 (so additional 8 address lines).

So not serial to parallel conversion.

Cheers from Oz,

zebity

Dave Wise:
Marked "DS1558D" is DS1558W which is 3.3V.  Its additional address lines are A11-A18.  It has eight extra registers you want to avoid, at 7FFF0-7FFF7.  Hold A11-A18 high except tie at least one to A3 so xx8-xxF hit the top bank while xx0-xx7 go elsewhere.  BF (Battery Flag) is not defined, but I don't think Tek cares.  Everything else is compatible AFAICT.

I will certainly want one sometime for my TDS3054B which retains data but the clock stops.

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