SUMMARY: SS10 MBus speed jumper settings

From: Sandiway Fong (
Date: Wed Oct 06 1993 - 16:02:40 CDT

I posted a query on Monday about the right motherboard jumper
settings for Sparc 10 Models 41 and 512MP which run at 40.33MHz
and 50MHz, respectively. The MBus runs either at 40 or at 36Mhz
(or 33Mhz for Model 20s?). My post was prompted by the fact
that I had to change jumper settings when upgrading from a
Model 41 to a 512MP which, theoretically, should NOT have been
necessary since both machines are capable of supporting MBus
operation at the full 40MHz.

Thanks to the readers of comp.sys.sun.hardware, I got a fair
number of useful email on this subject. It turns out my
SS10/41s (2 of them) had INCORRECTLY set jumper combinations,
i.e. the MBus was running only at 36MHz. This means Sun had
shipped both SS10/41s with the wrong setting.

Both of my machines were of the 3-jumper variety. Here are the
relevant settings for those wishing to confirm their settings:

Setting 1 (40MHz): J1401 (no jumper), J1403 and J1404 (1 to 2)
Setting 2 (36MHz): J1401 (jumper), J1403 and J1404 (2 to 3)

One strange twist to this whole story is that cputype, a script
that someone kindly sent me (which had been recently posted to
the net according to the sender), reported "SPARCstation 10
Model 41" for Setting 1, but reported that the MBus was
operating at 40MHz for Setting 2. This contradicts the Sun
Field Service Manual according to the email I received.

Thanks again for the help,


Dr. Sandiway Fong
NEC Research Institute Inc.
4 Independence Way
Princeton NJ 08540

(609) 951-2733 (609) 951-2482 (FAX)

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