PSI-MODEMSHDSL/SERIAL
1-6
PHOENIX CONTACT
104275_en_c00
1.5
Interface basics
1.5.1
RS-232
The RS-232 interface is a widely used serial interface, which is defined in standards EIA-
232 and CCITT V.24.
This interface carries out data exchange between two devices (point-to-point connection).
It transmits and receives data in full duplex mode over lines of up to 15 m. The maximum
transmission speed is 230.4 kbps.
In the simplest configuration, three cables are required:
–
TxD (transmit data)
–
RxD (receive data)
–
GND (common signal ground)
For more complex data transmission with hardware handshake, additional control and sig-
nal lines are required.
The RS-232 interfaces of devices can be designed as data communication equipment
(DCE) or data terminal equipment (DTE). In the case of a DTE device, data is transmitted
via the TxD connection, whereas a DCE device receives data via this connection.
A DTE device can be connected to a DCE device via a linear connection. When connecting
two devices of the same type (DTE/DTE or DCE/DCE), all cables must be crossed.
The SHDSL modem supports automatic switchover between DTE/DCE (see "Connecting
the serial interface" on page 2-9).
Figure 1-2
Pin assignment of the RS-232 interface for 25-pos. D-SUB (9-pos. D-SUB)
The signal level is defined as follows:
Data cables
-3 V ... -15 V for logic "1"
+3 V ... +15 V for logic "0"
Control/signal lines
-3 V ... -15 V for logic "0"
+3 V ... +15 V for logic "1"
Properties of RS-232
Standards
ITU-T V.24/DIN 66020-1, ITU-T V.28/DIN 66259-1, TIA/EIA-232
Transmission
speed
230.4 kbps, maximum
Transmission
length
15 m,
max.
(RS-232)
For industrial applications, we recommend reducing
the distance to 5 m at a high transfer speed.
Method
Voltage interface
Principle
Full duplex, point-to-point, no multipoint connection
PE
PE
1
1
2 (3)
2 (3)
3 (2)
3 (2)
4 (7)
4 (7)
5 (8)
5 (8)
6 (6)
6 (6)
7 (5)
7 (5)
8 (1)
8 (1)
20 (4)
20 (4)
TxD
TxD
RxD
RxD
RTS
RTS
CTS
CTS
DSR
DSR
GND
GND
DCD
DCD
DTR
DTR
DTE
DCE