Return to BSD News archive
Xref: sserve comp.os.linux.misc:30683 comp.os.386bsd.misc:4267 sci.electronics:85348
Newsgroups: comp.os.linux.misc,comp.os.386bsd.misc,sci.electronics
Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!bunyip.cc.uq.oz.au!munnari.oz.au!news.Hawaii.Edu!ames!ncar!newsxfer.itd.umich.edu!zip.eecs.umich.edu!newshost.marcam.com!news.kei.com!bloom-beacon.mit.edu!spool.mu.edu!umn.edu!mr.net!medtronic.com!rosevax!reddwarf!grante
From: grante@reddwarf.rosemount.com (Grant Edwards)
Subject: Re: 16550 detection
Message-ID: <1994Nov20.003058.12039@rosevax.rosemount.com>
Followup-To: comp.os.linux.misc,comp.os.386bsd.misc,sci.electronics
Sender: news@rosevax.rosemount.com (Rosevax USENET News auto-admin account)
Nntp-Posting-Host: reddwarf
Organization: Fisher-Rosemount, Rosemount Inc.
X-Newsreader: TIN [version 1.2 PL2]
References: <CMETZ.94Oct30051603@itchy.inner.net> <MICHAELV.94Nov1215132@MindBender.HeadCandy.com> <TYTSO.94Nov2113942@dcl.mit.edu> <JKH.94Nov2210122@freefall.cdrom.com> <Cyp34w.MxC@bonkers.taronga.com> <3a8u29$mi@awfulhak.demon.co.uk> <CzF7qx.9yH@indirect.com> <1994Nov18.082900.12223@slate.mines.colorado.edu>
Date: Sun, 20 Nov 1994 00:30:58 GMT
Lines: 31
Ade Barkah (mbarkah@slate.mines.colorado.edu) wrote:
: : In the days of 2400 bps/Baud modems, they were. A 2400 bps modem
: : transmits and receives (transcieves? ;^) two tones, one means "0"
: : and the other "1". If you use *more tones*, you can encode more than
: : one bit in each state change.
: Actually, I don't even think for 2400 bps modem 1 baud==1 bps.
: If I remember, the 2400 bps modems already use quadrature
: amplitute modulation (qam) encoding, with 600 baud/s at 4 bits
: per baud.
I think that's right. AFAIK, the highest bps==baud modems in common
usage were Bell 202, 1200 baud, mostly-half-duplex, FSK (1200/2200Hz?)
modems (they had a 75 baud FSK back-channel). Bell 103 was 300 baud,
300bps, full duplex, FSK. Bell 212 was 1200 bps, 300 baud, full
duplex, PSK, with seperate carriers for the A-party transmit and
B-party transmit. Each transmitted symbol consisted of a carrier
phase shift of 0, 90, 180, or 270 degrees.
After that, it gets pretty complicated with combined amplitude and
phase change for each symbol and both ends transmitting using the same
carrier frequency. It's darned amazing that anything past 1200bps
works at all -- and I still can't believe that color TV actually
works.
--
Grant Edwards |Yow! he dominates the
Rosemount Inc. |DECADENT SUBWAY SCENE.
|
grante@rosemount.com |