[ On Wed, November 4, 1998 at 16:13:46 (-0700), Chris Torek wrote: ]
> Subject: Re: PROM Pass: ?
>
> The Mostek chips are actually battery-operated-wristwatch chips.  By
> packaging the chip and a battery together, you get:
> 
>  - a BCD time-of-year clock (BCD because LCD watch displays use BCD
>    decoders)
>  - some battery-backed-up RAM
> 
> The latter serves as "EEPROM" and is infinitely writeable, unlike
> true EE/EA PROMs.  It also loses its memory when the battery goes
> dead.  If the battery is physically removable, this allows erasing
> the chip contents, but the ones I have seen are impossible to get
> at without destroying the Mostek chip.  (Kind of annoying, since the
> battery only lasts ~10 years.)

Yes, "infinitely" writable, but only for a period of ~10 years, i.e.
while the internal battery in the chip still has juice.  The battery is
completely and hermetically embedded in the clock/"EEPROM" chip.

Unfortunately when they do go dead you're completely toast until you get
a replacement, especially if you boot diskless!  ;-)

The same hybrid "chip" is used in the sparcstations too, but at least in
them it's socketed.

Contrary to earlier posts the host-id FAQ *does* contain information
pertaining to the Sun 4/xxx series machines.  To quote the relevant
part:

   The sun4 machines (e.g. Sun 4/1xx, 4/2xx, 4/3xx, etc.) also have
   M48T02 chips. These chips do not store the hostid and ethernet
   address, which are in an actual PROM, but they do keep track of the
   time of day and the system configuration information. Replacing the
   NVRAM chip is a relatively simple matter, the only trick is to set the
   appropriate values in the Sun PROM monitor using the q command then
   boot the operating system to kick-start the clock. You can use the
   table for the Sun 3/80 to set the values in the old Sun PROM monitor.
   The only significant difference is that normal/diagnostic boot is
   controlled by a physical switch instead of the byte at location 0x70b.
   See the Sun Hardware Reference (referred to above), your machine
   documentation, or the Sun FE Handbook if you need more information on
   the Sun PROM monitor.
   
I presume the PROM password must be stored in the NVRAM chip on these
machines, since it's part of the "system configuration information".

I.e. to change the password this chip must be replaced if it cannot be
re-programmed some other way such as with the instructions in the FAQ,
or with the SunOS "eeprom" command (the ability to do the former may
rely on the version of firmware, and the latter will require booting
with the currently programmed device and filename).

I don't have a the necessary documentation to give you the reprogramming
details (eg. my "Sun F.E. Handbook") unpacked yet, but someone on this
list must have a copy handy on a nearby shelf.

-- 
							Greg A. Woods

+1 416 218-0098      VE3TCP      <gwoods@acm.org>      <robohack!woods>
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