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Tech Stuff - RS 232 & ITU Alphabet Soup

This section describes the various RS-xxx (more properly TIA-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.

Note: Until February 11th, 2011 these specs referenced a EIA/TIA number (sometimes even a TIA/EIA number). EIA is no more. TIA has taken over its functions (for the Telecomms sector). Thus all specs should reference TIA, for example, TIA-232 etc.. Since this is the third change in recent memory (RS -> EIA/TIA -> TIA) it is probably bettor to stick with the RS terminology. Technically it is incorrect but it is stable!

Contents

1. TIA (RS) Complete Standards
2. TIA (RS) Electrical Standards
3. ITI V.XX Standards

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.

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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.

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 (as long as both ends are the same, obviously), the third pin carries a GND.

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ITU V.XX Standards

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

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