In <Pine.BSI.3.96.971223125426.17151N-100000@pillbox.broder.com>
jeremy@broder.com wrote:

> two, while the other is left alone.  These two paths then meet up at a
> jumper on the board, close to the CPU.  (It's labeled '20 40'.)  The 3/80
> ships with a shorting block (jumper) on the 20 MHz side, but you can
> easily move it to the 40MHz side.  (I have measured the 40 side with an
> oscilliscope and it is indeed 40 MHz, if you're worried.)

I think the jumper switches only FPU clock.
It is mentioned somewhere in Sun Hardware Reference Page:
http://sun-www.picarefy.com/

I had moved my 3/80's jumper on the 40 side with 20MHz 68030 and
40MHz 68882, it had worked fine. 

SunOS mc68881_version command showed the FPU clock is 40MHz,
but whetstone score was improved only 20% under SunOS :-(
I have no longer had the 3/80 so I cannot test it on NetBSD/sun3x,
but NetBSD/sun3x had worked on the 40MHz clock FPU 3/80.
---
Izumi Tsutsui
tsutsui@ceres.dti.ne.jp