> "der Mouse" <mouse@Rodents.Montreal.QC.CA> wrote:


> > OK, this seems like a decent time to bring up a question: I have a
> > block of SS2s with dead NVRAMs.  Searching on ebay, I found some Sun
> > NVRAMs, but they were marked as being for SS5/SS10/SS20.  Is there
> > actually any difference between an SS2 chip and an SS5 chip?
>
> I can't answer that at the moment, but I can say that there seem to be
> only two chips used, the M48T02/M48T12 and the M48T08/M48T18.  In my
> experience, you can freely swap among machines that use the 02/12 and
> among machines that use the 08/18, needing at most to rewrite the

*Ideally*, you would prefer the 0x version of each device.  I think the 1x
versions have a *lower* battery switchover threshold... depending on how
rapidly Vcc decays in the processor, it is conceivable that the CPU
can freak out *before* the BBSRAM has decided that it should write
protect it's contents (from an errant CPU).

Turning off the oscillator hardly seems worthwhile -- unless you have
an excess of spare time available  :>  I believe the devices are guaranteed
to operate for 10 years IN THE ABSENCE OF POWER.  Even with
the oscillator disabled, the BBSRAM still draws power and the "battery"
still has self-discharge characteristics.  (These are aggravated with
temperature).  Personally, I find it annoying to have to remember to reset
the clock if I take a machine out of storage...  and, the battery is *still*
going to fail at *some* point  (i.e. just attach a whopping BIG battery
to the device and forget about it...)

> contents (mkpl is your friend :-).  Since the former is a 24-pin chip
> and the latter a 28-pin, they are physically incompatible, which means
> that (if I'm right) you can use any chip that's physically compatible.

I have found that chosing MAC addresses of the form  x:x:x:a:x:!a
(et al.) makes it easier to program the BBSRAM -- since the checksum
doesn't change from one machine to the next (one less byte that has to
be computed!)

> Once I get home tonight I'll be able to check; I have a 2 and a 5 that
> I can open up and look at the pin count for.