Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!oberon!skat.usc.edu!blarson
From: blarson@skat.usc.edu (Bob Larson)
Newsgroups: sci.electronics
Subject: Re: Beyond Asynchronous RS-232...
Message-ID: <15554@oberon.USC.EDU>
Date: 26 Feb 89 09:28:16 GMT
References: <315@cfcl.UUCP>
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Reply-To: blarson@skat.usc.edu (Bob Larson)
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In article <315@cfcl.UUCP> dwh@cfcl.UUCP (Dave Hamaker) writes:
>I have an idea for serial communications which sounds good to me, but
>as a software type I'm not sure if it makes sense from an electronics
>perspective.
>
>As background, there is a tendency to denigrate asynchronous communi-
>cations as being 20% slower than synchronous communications because of
>the start/stop bits required for each character in the former.

While this is true, actual bits/second over a piece of wire is rarely
a limitation.  Just specifying better wire will get you up to at least
the hundreds of megabits per second range.  (Coax)

A guarenteed, completely out of band flow control is MUCH more important.
Modems and such that are woried about a few percent eficency could use
this converting from async to sync.

>I think automatic speed detection can profitably be included.

If your going to spec a new protocol, you might as well specify exactly
one speed and use the out of band flow control.

The new protocol should be symetrical and include flow control,
dtr/dsr, cd, etc without extra wires.

>I think I would
>change the cabling scheme to use 4-wire modular telephone-style
>connection.

These connecters are TO common to be considered.  Most computers
wouldn't like the 100 VAC ring signal from a phone, and the phone co.
wouldn't like you shorting out their wires.  Since (most) phones don't
care about wiring polarity, you'll probably find many existing cables
don't have the needed twist.  (Not to mention the 2 wire cables.)
Phone connectors don't support shielding.  Good features of the phone
connector include: cheap, easily available. 

I kind of like the idea of an androginous connector, so all cables may
be used as extentions.  (The connector would have a male and a female
side.)  

I'd specify:

cable: two sheilded twised pairs, shileds isolated from each other.
Sheilds are a nessesity now that the FCC has cracked down
on RFI.

connector: (see above, I havn't found a real one I like)

Transmiter: balanced, signal levels specifed so it can be driven from
a single 5v power supply.  Must respond to flow control within 2
characters.

Receiver: opto-isolated, must detect loss of transmission signal (both
lines at the same potentional) and force the transmitter to send same
back for at least 1 second and reset all compunications paramaters to
the defaults.  Must accept 256 characters after sending flow control.
(This allows 38 ms of transmission delay, enough for the local lines
this is speced for.)

Speed: 64k bits/second

Both sides must be implemented for flow control, etc. even if all data
transfer will be in one direction.

More out of band signals to negociate error correcting protocol, etc.

>How doable is this?

The hard part is getting anybody else to implement it.

The ANSI commitee that did RS422/RS423 obviously didn't understand
what was wrong with RS232c.  (25 pins is WAY too many, so they go to
37 plus an optional 15!)

>-Dave Hamaker
>...!ucbvax!ucsfcgl!hoptoad!cfcl!dwh
Bob Larson	Arpa: Blarson@Ecla.Usc.Edu	blarson@skat.usc.edu
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