5. Hardware Specification

5.1. Definition of Interchange Circuits

The interchange circuits conform to CCITT recommendation X20

Interchange	Interchange
Circuit Num.	Name

G		Signal ground or common return
Ga		DTE common return
Gb		DCE common return
T		transmitted data
R		Received data

5.2. Electrical Characteristics

The electrical characteristics conform to CCITT recommendation V.11 (X.27/RS422/RS485) "Electrical characteristics for balanced double-current interchange circuits for general use with integrated circuit equipment in the field of data communications".


Despite that statement, quite a few system use V24/RS232; Gordon

5.3. Connector Specification

The connector specification conforms to ISO 4903, 15 way 'D' type.


Don't trust that people comply to that. Many are 9 or 25-way 'D' types; Gordon


Pinout is defined in ISO4903, not sure how widely used (we had a 25-way D-type with other services on it also); Gordon

5.4. Audio Signals

600 Ohms balanced with respect to earth, Signal adjustable between -6dBm and -20dBm.


Many (most?) systems working via Espa 4.4.4 have no speech or speech paths; Gordon

5.5. Baud Rates

All standard Baud rates between 300 and 9600 are available.


I think most default to 1200; Gordon