Revised proposal on MSE high-impedance spec

John Lohmeyer lohmeyer at
Mon Jun 21 11:05:46 PDT 1999

* From the T10 Reflector (t10 at, posted by:
* John Lohmeyer <lohmeyer at>
At 6/21/99 10:56 AM , Gene_Milligan at wrote:
>The new figure allows an input current to all SCSI devices of >10 ma or
>>160 ma on the bus. This is wrong.


Yes, that much current could flow if a device was capable of sourcing it.
New devices are not permitted to source anywhere near that much current.
Some legacy devices might be able to source more current above 3.0 volts,
but probably not anywhere near 160 mA.  We may have to say that devices
that source more than x mA above 3.0 volts are not permitted on a SPI-3
SCSI bus.

The May SPI-3 working group felt that this proposal represented a
reasonable trade-off between accommodating legacy devices and the need to
permit new devices to use 3-volt processes.  If we do not allow these new
devices to clamp excessive currents above 3 volts, then the pad designs
will be much more difficult and expensive.


John Lohmeyer                  Email: lohmeyer at
LSI Logic Corp.                Voice: +1-719-533-7560
4420 ArrowsWest Dr.              Fax: +1-719-533-7036
Colo Spgs, CO 80907              BBS: +1-719-533-7950

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