[time-nuts] Dallas NV-SRAM replacement? (in 3458A)

Poul-Henning Kamp phk at phk.freebsd.dk
Tue Jun 8 18:05:32 UTC 2010


In message <20100608164407.A9783112AD9 at mail.ebirds.it>, Marco IK1ODO -2 writes:

>Speaking of the 3458A, it has three DS1235Y-150 non volatile SRAM on 
>the CPU board. Each is a 32K x 8 bit, so there is a lot of info inside.
>As the useful life of those is in the order of 10 years and most 
>3458A a re now 10 to 20 year old, is there a possible replacement? 
>Possibly with a more modern component?

I replaced all the NVRAM's in mine last month, no issues.

There are plenty of NVRAMs to be had as new.

>Also, of course it would be a good idea to read and save the contents 
>of the SRAMs before replacing, but... is any custom data in them that 
>cannot be rewritten with a complete recalibration?

The CALRAM contains a number of "magic" counters, one of which is
called "destructive overloads" that a calibration cannot possibly
restore.

But from a functional point of view: no.

You can read out the memory with the undocumented "MREAD" command,
but the CALRAM is protected by various tricks, so you cannot just
use the MWRITE command to restore it.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.




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