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SUN NVRAM alternate battery clock chip


Jun 27, 2019
Vancouver WA
I recently purhcased an Sun Ultra 5 workstaion, and it as expected had a dead NVRAM clock chip. The one in it is a ST M48T59Y-70PC1D, these are no longer available and cost of $50 from other sources (ebay, Sun recycle businesses). There is a hack where you grind down the chip expose the battery terminals and solder a button battery holder for a CF232.

I do not have a dermal or a good soldering iron, so ordered from digitkey an ST M48T58Y-70PC1


this cost around $17.

I installed this in my Ultra 5 reconfigured the NVRAM and it works.

The M48T58Y is nearly identical to the M48T59Y, One has an extra enable in the place of the RST/IRQ. Seems these are not used. The documentation on both chips in near identical accept for the 2 pin changes.

to program the NVRAM on the boot prompt I typed in

you will need to get the machine type

01 2/1x0
02 2/50
11 3/160
12 3/50
13 3/2x0
14 3/110
17 3/60
18 3/e
21 4/2x0
22 4/1x0
23 4/3x0
24 4/4x0
31 386i
41 3/4x0
42 3/80
51 SPARCstation 1 (4/60)
52 SPARCstation IPC (4/40)
53 SPARCstation 1+ (4/65)
54 SPARCstation SLC (4/20)
55 SPARCstation 2 (4/75)
56 SPARCstation ELC
57 SPARCstation IPX (4/50)
61 4/e
71 4/6x0
72 SPARCstation 10 or SPARCstation 20
80 SPARCstation Classic, LX, 4, 5, SS1000, Voyager, Ultra 1, Ultra 2, Ultra 60/80, Ultra 5/10/30, Blade 100/150

next you will need you hostid (this is on the yellow label on the old M48T59Y being replaced, it is a 6 digit hex number).

so for example if I was going to program an Ultra 2, with host ID DF56A4 I would enter the following
setenv diag-switch? false

1 0 mkp
80 1 mkp (this is the real machine type)
8 2 mkp
0 3 mkp
20 4 mkp
df 5 mkp
56 6 mkp
a4 7 mkp
0 8 mkp
0 9 mkp
0 a mkp
0 b mkp
df c mkp
56 d mkp
a4 e mkp
0 f 0 do i idprom@ xor loop f mkp

After you have typed this it will appear to hang on some systems, it has not enter ^D ^R (control D, control R) to drop down to the command OK prompt.

To verify the all is well type .idprom

should print out Mac and host with a checksum of 29

for more information see (this is where I got this information)



Mar 17, 2020
I just got done doing the exact same thing to my Sparcstation 5 (not ultra) which is a bit older but the DigiKey M48T08-150 worked fine and was about the same price you paid.
I followed the steps to reprogram and it works perfectly.


Jun 27, 2019
Vancouver WA
Do Not use the ST M48T58Y-70PC, it is not compatible with the SAB SAB82525 controller. This can result in pin 1 or 68 being pulled low and invalidating memory banks. which will lead to watchdog exception or red state exception .

I did find a US suppler of M48T59Y-70PC1D on ebay for under $9. I will post an update when I get the new NVRAM chip.