🚀 go-pugleaf

In article <PAISLEY.89Sep7122146@lobotomy.cme.nist.gov> 
paisley@cme.nist.gov (Scott Paisley) writes:
> Does anyone know if the NuBus slot are still at 10Mhz?  It would seem
> to me that faster slots would be a great selling point.  Especially if
> apple is planning on make the IIci there mainstream machine.

The answer is no, not ever ... and yes, maybe.  To explain ...

1)  NuBus must always have a fundamental clock rate of 10 MHz or existing 
cards will fail.  It is also *extremely* difficult to get a synchronous 
bus to run much faster without drastic increases in system cost *for all 
cards*.  The major difficulty is getting the arbitration and bus 
turn-around (going from writing the address to reading the data) to run 
faster.  Note that Next only runs their Nubus-similar system at 12.5 Mhz, 
which is not enough of an improvement for us to obsolete everything in 
sight.

2)  HOWEVER, it still may be possible to run data bursts faster than the 
current 10 MHz.  This is what Next does to get the 25 MHz burst rate ... 
effectively sending two words for each 12.5 MHz clock.  There are 
currently two proposals before the IEEE P1196-R (NuBus Revision) working 
group that do just that ... effectively getting a 20 MHz data burst rate.  
These proposals are coming from Supermac and E-Machines people, and are 
both quite compatible with existing cards.  The big change will have to 
come in Mac CPU's:
     a) The existing unused (and shorted together) -5.2V lines will have 
to be nuked (You weren't using them, were you?) and reallocated to other 
functions. 
     b) At least two of these recycled signals are used for a new clock 
line and a special mode indicator.

The first detailed discussion of these proposals will be done at the next 
1196 meeting in the Boston area next week.  The working group is trying to 
get a draft of the revision finished by Christmas.

****There is absolutely no commitment by Apple to do anything about any of 
these proposals.****

---- Michael Teener -- 408-974-3521 -- IEEE P1196-R Secretary -------+
---- Internet teener@apple.com, AppleLink TEENER1                    |
---- Apple may know my opinions, but *I* am responsible for them     |
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