Technical data

www.westermo.com Theoretical and general applications 25
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Signals in V.24/RS-232-C
Pin V.24 RS-232 Signal Signal name Direct.
9/25 Code Code DCE
1 101 AA GND Protective Ground –
3 2 103 BA TD Transmitted data I
2 3 104 BB RD Received data O
7 4 105 CA RTS Request To Send I
8 5 106 CB CTS Clear To Send O
6 6 107 CC DSR Data Set Ready O
5 7 102 AB SG Signal Ground –
1 8 109 CF DCD Data Carrier Detector O
9 – – canbe+12V –
10 – – can be – 12 V –
11 126 SCF STF Select Transmit Frequency I
12 122 SCB Secondary DCD O
13 121 SBA Secondary CTS O
14 118 SBA Secondary TD I
15 114 DB TC Transmit Clock O
16 119 SBB Secondary RD O
17 115 DD RC Receive Clock O
18 – – – –
19 120 SCA Secondary RTS I
4 20 108/2 CD DTR Data Terminal Ready I
21 110 CG SQD Signal Quality Detect O
9 22 125 CE RI Ring Indicator O
23 111 CH/CI Data Signal Rate Selector O
24 113 DA EC External Clock I
25 133 – RFR Ready For Receiving I
Bold type indicates the most common signals in local communications using short-
haul modems. Direction I/O indicates the direction to/from the modem (DCE)
where I is an input and O an output. Accordingly, the TD (Transmit Data) signal is
the output in a DTE yet the input in a DCE. The definition of DCE and DTE is one of
the most common sources of error, when these are linked to RS-232 equipment, see
page 26.
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