[SunRescue] sun3/80 scsi

[jeff borisch]

Greg A. Woods wrote:

> [ On Thursday, December 28, 2000 at 14:46:51 (-0500), jeff borisch wrote: ]
>> Sorry to be dense but what is the polarity are you referring to? Does it
>> have something to do with connecting the ribbon cable backwards? You know,
>> the mistake that is easy to make if you have the cheezy connectors without
>> the the key molded into it.
> 
> No, not the connector orientation -- just the polarity of the voltage
> supplied for TERMPWR.

I see, it occurred to me that it could mean that too. But it seemed that
such a thing would be part of the scsi specification, like the voltage and
polarity of the data signal is a standard.

> All you need to worry about is whether or not your system has the
> correct polarity power out on TERMPWR, and that it's not connected to
> GROUND.

When you say "system" I think of the mainboard or the scsi controller.
I have only seen jumpers on drives to supply TERMPWR to the bus. But from
reading the SCSI FAQ, I learned the initiator (the mainboard SCSI controller
in the 3/80s case) also is supposed to apply voltage to this line.

Is it common to have devices that supply mismatched TERMPWR? I have never
seen the voltage or polarity for TERMPWR listed on any drive specsheet.

> Oh, and one model, 530-1874-02, of the Sparc-10 motherboard has the
> TERMPWR line grounded on the internal cables too, but enabling TERMPWR
> on an internal drive will supposedly "only" trip the PS current limiter....
> 
> Of course you should never need TERMPWR enabled on an internal drive
> anyway, since there's no terminator to power on a stub.  :-)

Of Course (-: , I guess this is Sun's way of making sure one never makes the
same mistake twice.

Thanks again,
Your writing make more sense than anything else I've read about this.

--jeff

 


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