[rescue] Survey: what do you want in _your_ SPARC?

[Joshua D Boyd]

On Fri, Jul 19, 2002 at 01:04:24PM -0400, George Adkins wrote:
> > Yes, I'm learning that different is often the case, with this system.
> > Frinstance the memory bank layout is unique, and I recall reading somewhere
> > that SS5s don't require termination for internal drives but this Axil
> > definitely does.  
> 
> Umm, the SS5  drives are SCA.  One normally cannot terminate SCA drives, the 
> backplane provides termination.

That might be why internal termination isn't required then.
 
> You may be thinking of the SS2.  In an SS2, the motherboard provides 
> termination, as the SCSI bus is actually in the traces on the board.  The 
> ribbon cables are actually stubs (which is why they have to be very, very 
> short.)  The external tail of the bus usually remains unterminated.  Because 
> the signalling rate is slow (only 5 MB/sec), and it is very short (maybe 200 
> mm), the bus can function adequately with only half-termination.  The 
> confusion with these guys comes from the fact that if you put a single, 
> terminated drive in them, (without any external devices attached) they will 
> still work, because you now have a fully terminated bus (although it's 
> concentrated all at one end.)  However, if you put a terminated drive in them 
> and then terminate an external leg of the bus, you are now triple-terminated, 
> and you can have problems maintaining the signal on the bus, leading to 
> headaches. 

Interesting.  I never knew that about my SS2.  When I rebuild it[1], I'll
have to keep that in mind.

-- 
Joshua D. Boyd

[1] I really love this machine, but I think I'm going to give it to
someone who needs some sort of machine like that, then keep my eyes
open for a new one.