Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!cis.ohio-state.edu!ucbvax!mtxinu!taniwha!paul
From: paul@taniwha.UUCP (Paul Campbell)
Newsgroups: comp.arch
Subject: Re: ACE (Was Re: Will NeXT survive?  Grow with the times?)
Message-ID: <863@taniwha.UUCP>
Date: 5 Jun 91 07:22:10 GMT
References: <11399@uwm.edu> <32580026@hpcuhe.cup.hp.com> <4638@batman.moravian.EDU> <22152@cbmvax.commodore.com>
Reply-To: paul@taniwha.UUCP (Paul Campbell)
Organization: Taniwha Systems Design, Oakland
Lines: 37

In article <22152@cbmvax.commodore.com> daveh@cbmvax.commodore.com (Dave Haynie) writes:
>In article <4638@batman.moravian.EDU> halkoD@batman.moravian.EDU (David Halko) writes:
>>> peter da silva writes:
>>> Is this true?  I understand that NeXT uses a 25MHz NuBus (2.5 times the NuBus
>>> used in the Mac II series).  
>
>Actually, I've heard both that the NeXT uses a 25MHz NuBus clock and that it
>uses a 12.5MHz NuBus clock.  Anyone know for certain?

Yeah, they do both, the basic bus is a 12.5MHz NuBus (12.5/25 is a 'nice'
number if you have a 25MHz CPU - everything is synchronous) - they have a
special burst mode which is clocked at 25MHz - the bus has 2 clocks 12.5/25.

NuBus 90 has picked up the Next clocking/burst scheme (it is a nice design)
and added it to existing NuBuses at 10/20MHz (for compatability).

>>A 25 MHz backplane is a quick backplane, definitely not slow! The analog bus,
>>while superior in many ways, doesn't mean that it is any slower. I syncronous
>>25 MHz bus and asyncronous 25 MHz bus should be about the same speed, but
>>the analog bus should be slightly slower due to the handshaking needed which
>>is not required for the syncronous bus. Am I off target here?

Next solve this by driving everything with the CMOS driver ICs, having short
backplanes and requiring the driver/controller chips to be physically right
next to the bus. The also terminate it so that it gets exactly one reflection
within the bus settling time.

I don't work for Next, I'm just a poor NuBus designer who has to keep up
with the world :-)

	Paul Campbell

-- 
Paul Campbell    UUCP: ..!mtxinu!taniwha!paul     AppleLink: CAMPBELL.P

My son is now 2 months old, in that time he has doubled his weight,
if he does this every 2 months for the next year he will weigh over 300lbs.