🚀 go-pugleaf

I said earlier that SCSI ids above 7 are disallowed.  The standard
implies this repeatedly, but I couldn't find anything that says
so explicitly -- the closest was the sentence from the foreword
I quoted before.

Besides which, I now have to retract part of my statement (about there
being no implementations of arbitration logic above id 7). The
data book for for the NCR 53C720 (their 16-bit SCSI-2 processor)
says it will allow you to specify an ID of up to 15. 8-15 are lower
priority than 7-0.  So, at least one vendor is building toward
the future. The priorities, from highest to lowest, are
7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8.

I hadn't thought of putting 15-8 below 7-0; this would allow mixed
busses to work correctly (those which arbitrate with only 8 bits
will always get priority over anything higher, so they don't even have 
to know the higher ones exist). of course, in a mixed bus, not
all devices can talk to each other, so having them share the bus
makes little sense anyway. 

A device which arbitrates with only 8 bits can never select a
device with an id of 11, for example.  The id 11 device can select
an id 5 device, but cannot allow it to disconnect for fear that
it will be unable to reconnect. Also, if the target (id 5) depends
on knowing the id of the initiator, (11), it will believe that
id is 0.

I have heard that the NCR 53C720 is available in the U.S., but
it's not yet here (I'm in Japan, dewspite the email address).
Anybody know which computer manufacturers will be first to market
with 16-bit SCSI? We're building a device with a need for
speed (to quote Tom Cruise).

Speaking of making sense, am I making any?

		--Rod