Xref: utzoo comp.sys.ibm.pc:30496 comp.periphs:1846 comp.misc:6391
Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!att!mtunb!dmt
From: dmt@mtunb.ATT.COM (Dave Tutelman)
Newsgroups: comp.sys.ibm.pc,comp.periphs,comp.misc
Subject: Re: RS-232 protocol primer (long)
Message-ID: <1538@mtunb.ATT.COM>
Date: 23 Jun 89 12:24:32 GMT
References: <589@megatek.UUCP>
Reply-To: dmt@mtunb.UUCP (Dave Tutelman)
Organization: AT&T Bell Labs - Middletown, NJ
Lines: 49

In article <589@megatek.UUCP> hollen@megatek.UUCP () writes:
>
>			Serial Protocols

Thanks, Dion, for a really good tutorial!

The only nit I'd like to pick is your subject line's suggestion
that this has anything to do with RS-232.  (The retitling to
"serial protocols" is appropriate, and "asynchronous protocols"
or "ASCII protocols" would be even more so.)

In fact, your comment about the RS-232 standard itself needs some
corrections...

> The RS232 "standard" is merely a document which designates
>the accepted use of the 25 wires in a cable and the physical configuration
>of the size and shape of the connector (DB-25). 

Why is the word STANDARD in quotes?  There is, in fact, a REAL LIVE
EIA standard, designated RS-232-C and dated 1981.  (Originally 1969,
reaffirmed 1981.)  It DOES NOT specify the DB-25 interface connector,
or any interface connector at all.  It DOES specify:

   -	Scope of applicability (e.g.- speeds to 20 kilobits/sec).
   -	Electrical characteristics (e.g.- driver & receiver voltages
	and impedances).
   -	Functional descriptions of the leads, including extensive
	"rules" of how they MUST be used (to comply with the standard).
   -	Some standard subsets of the full 25-lead interface.

>Many implementors make
>unique use of the signals on the wires, and of the data sent over them.
>There are some commonly accepted followed conventions, but always be
>aware of someone having implemented them "almost" like you would expect.

Most of the "conventions" to which you refer are in fact specified by the
functional rules in RS-232-C.  Some of the "unique uses" are in
direct violation of the standard, though most are permitted (or even
encouraged, if you read the standard closely).

Once again, thanks for a really good tutorial on asynchronous ASCII
protocols (which have nothing to do with RS-232).

+---------------------------------------------------------------+
|    Dave Tutelman						|
|    Physical - AT&T Bell Labs  -  Middletown, NJ		|
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