Some Alphabet Soup

This section describes the various RS-xxx (more properly TIA/EIA-xxx) standards and some of the V.xx standards from our good friends at the ITU (did we really say that - they are the guys who still charge for specs!).

A partial apology: The ITU, bless their hearts, now have a policy that you can get two docs for free when you sign up. It's a start but why don't they do like the IEEE 802 guys. Free but only after 6 months. If you are desperate you pay, if not you wait.

Contents

EIA/TIA (RS) Complete Standards

EIA/TIA (RS) Electrical Standards

ITI V.XX Standards

EIA/TIA Standards (a.k.a. RS)

EIA/TIA defines Complete and Electrical standards.

Complete Standards

Complete standards may define the electrical characteristics or they may call up one or more Electrical standards. They always define a connector since they are supposed to be complete.

Name	Electrical	Ref	Connector	Description
RS 232	RS-232	E	DB25	Unbalanced point-to-point serial interface on a DB25 connector. Max. official data rate 20Kbps (really).
RS 449	RS-422-B RS-423-B	-	DB37	Balanced multi-drop serial interface on a DB37 connector. Max data rate 2Mbps. Not quite the biggest connector in the world - that goes to the old ITU V.35 connector but... Sensible people use 530-A instead.
RS 530	RS-422-B RS-423-B	A	DB25	Covers Balanced (RS-422 and RS-485), multi-drop (RS-485) and unbalanced (RS-423) serial interface on a DB25 connector. Max data rate 2.1Mbps.
RS 561	RS-562	-	RJ45 (MJ8)	Unbalanced point-to-point serial interface on a RJ45 (Modular Connector 8 positions). Max. data rate 38.4Kbps.
RS 574	RS-232	-	DB9	Unbalanced point-to-point serial interface on a DB9 connector. Max. data rate 20Kbps (really).
RS 613	RS-612	-	?	Balanced point-to-multipoint serial interface on a ? connector. Max data rate 52Mbps.

EIA/TIA Electrical standards

These are Electrical standards and are not Complete that is, they do not define signal names. They are typically referenced in a complete standard. Table below highlight the major characteristics.

Name	Min Signal	Max Signal	Out Imp	In Imp	Comments
RS-232	+- 3V	+- 25V	300	3K - 7K	Unbalanced point-to-point.
RS-562	+- 3V	+- 25V	300	3K - 7K	Unbalanced point-to-point.
RS-422-B	+- 7V	+- 12V	100	4K	Multi-drop balanced driver and receiver. Max. of 1200 meters all terminals, max of 500 meters between any two terminals.
RS-423-B	+- 7V	-	-	-	Multi-drop unbalanced driver and balanced receiver
RS-485	+- 7V	+- 12V	-	-	Multi-point balanced driver and receiver. Max of 1200 meters all terminals, max of 500 meters between any two terminals. Up to 32 stations/terminals assuming 12K load. Lower load allows more terminals.
RS-612	-0.5V	+2V	-	-	Balanced driver and receiver. Max differential <= 1.5V.

Notes:

• RS-485 is frequently used as a simple three wire system in many half-duplex, multi-dropped environments with TX and RX being alternately switched onto the same two pins - it does not matter whether they are the TX or RX pair, the third pin carries a GND.

ITU V.XX Standards

The ITU, the 500 pound gorilla of the standards world (and the guys who still charge for specs).

Name	Electrical	Description
V.24	V.28	Defines the signal names used in serial interfaces. Connector defined in ISO 2110 and ISO 4902. Practically the same as RS-232
V.28	-	unbalanced point-to-point serial interface. Practically the same as RS-232.
V.35	-	Term still widely used but standard withdrawn years ago and replaced with V.10 and V.11. Still holds the record for the biggest connector known to man-kind the infamous CCITT 37 pin connector. Mostly uses a DB25 connector today but not every manufacturer uses the same wiring standard.
V.10	-	unbalanced driver and balanced receiver point-to-point serial interface (a.k.a RS-423-B).
V.11	-	Balanced driver and receiver point-to-point serial interface (a.k.a. RS-422-B).

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