mark@mips.COM (Mark G. Johnson) (12/20/89)
Seen on page 33 of the December 18, 1989 issue of EE TIMES
... Augat product manager Mike Prisco ...
"All high-speed logic is going to need 50 ohms"
--
-- Mark Johnson
MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086
(408) 991-0208 mark@mips.com {or ...!decwrl!mips!mark}myers@hpfcdj.HP.COM (Bob Myers) (12/22/89)
> Seen on page 33 of the December 18, 1989 issue of EE TIMES > > ... Augat product manager Mike Prisco ... > > "All high-speed logic is going to need 50 ohms" Yup. And clearly in the context of high-speed logic requiring controlled- impedance PC boards and connectors. So what's wrong with that? Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers%hpfcla@hplabs.hp.com | sentient life-form on this planet.
mark@mips.COM (Mark G. Johnson) (12/28/89)
>> Seen on page 33 of the December 18, 1989 issue of EE TIMES >> >> ... Augat product manager Mike Prisco ... >> >> "All high-speed logic is going to need 50 ohms" > > >Yup. And clearly in the context of high-speed logic requiring >controlled-impedance PC boards and connectors. So what's wrong >with that? Yow, lack-o-smileys lamentably impedes universal understanding (again). As C programmers, ask yerselves "why is there a magic number (50) embedded up there?" That's the joke, ladies und gents --- the quote above, read contrapositively, says, "if it isn't 50 ohms then it cannot be high speed logic". When stated this way, do you agree? Is 60 ohms truly a not-high-speed characteristic impedance? How about the Cray-1 with its 90 ohm characteristic impedance "mat"? (Or for that matter, the CDC 6600 and its 75 ohm coax). What about the folks at Tektronix who claim a Futurebus+ backplane will sustain 500 MBytes/sec (note: Futurebus+ != 50.0 ohms). Why does the number 50.00 inspire such closed-minded religious zeal? Should we indeed publicly preach that 60 ohms is considered harmful, and 40 is Right Out?? Are Cray and CDC either badly-designed, or not-fast?? Letting out a year-end harrumph, -- -- Mark Johnson MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086 (408) 991-0208 mark@mips.com {or ...!decwrl!mips!mark}