A-22
A2
A2.2
RS-232 STANDARD
In 1963, the Electronic Industry Association (EIA) established a
standard to govern the interface between data terminal equipment and
data communication equipment employing serial binary interchange.
The latest revision of this standard (RS-232) has been in effect since
1969 and is known as RS-232C. It specifies:
-
Mechanical characteristics of the interface
-
Electrical characteristics of the interface
-
A number of interchange circuits with descriptions of their
functions
-
The relationship of interchange circuits to standard interface
types
The specification does not mean that two devices that are RS-232
compatible can be connected together with a standard cable and
be expected to work.
Mechanically, RS-232 interfaces use a 25 pin male connector (DS-
25P) with the data terminals and a 25 pin female connector (DS-25S)
with the data communications units (modems).
Electrically, RS-232 signals are bipolar and are referenced to a
common ground (AB) on pin 7. Transmitted signals must be between
+
5 and
+
15V or -5 and -15V into 3000 to 7000 ohm loads. Maximum
open circuit transmitter outputs is
±
25V. Logic levels are:
+5 to +15V
-5 to -15V
Data
0
1
Control
1 (On)
0 (Off)
