Ascotel IntelliGate 2025/2045/2065
788 Cabling interfaces Part 4
7.5 Special Interfaces
7.5.1 V.24 Interface
V.24 standard
V.24 is a serial interface used for connecting a printer or PC. In accordance with
the V.24 recommendation, a cable length of 15 m limits the transmission speed
to 38 400 bit/s. The system's maximum transmission speed is 115200 bit/s. The
cable length must not exceed 2 m. Transmission errors can occur if these limits are
exceeded. A current loop converter (TTY) has to be used if the cable length is
insufficient. Cable lengths of up to approx. 1 km are possible with this interface.
Two types of equipment can be connected to the V.24 interface:
• DCE: Data Communication Equipment
• DTE: Data Terminal Equipment
The pin assignment differs according to the type of equipment used.
Signals are specified as follows:
Tab. 4.46: V.24 signals
A straight connecting cable (modem cable; straight) must be used when connect-
ing DTE-type equipment with DCE-type equipment (e.g. PC → modem,
modem → PC).
A null modem cable must be used when connecting equipment of similar type
DTE – DTE (e.g. PC→PC). The null modem cable is crossed.
Signal Pin Signal direction CCITT stand-
ard V.24
Name / function
D-Sub-9 D-Sub-25 DTE DCE
TXD 3 2 out in 103 Transmitted Data
RXD 2 3 in out 104 Received Data
RTS 7 4 out in 105 Request To Send
CTS 8 5 in out 106 Clear To Send
DTR 4 20 out in 108 Data Terminal Ready
DSR 6 6 in out 107 Data Set Ready
DCD 1 8 in out 109 Data Carrier Detect
SGND 5 7 — — 102 Signal Ground
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