[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

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.

More information about the time-nuts mailing list