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Serial Cable Pinouts
There are two types of serial cable connection in the RS232 standard,
DTE connections and DCE connections. DTE stands for Data Terminal Equipment
and DCE stands for Data Communications Equipment. DTE connections are
what are on the serial port of a PC. A DCE connection is similar to a DTE connection except
that the Transmit & Receive, DTR & DSR, and
RTS & CTS pin connections are switched.
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25 Pin Connector on a DTE device (PC connection)
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Male RS232 DB25
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Pin Number
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Direction of signal:
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1
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Protective Ground
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2
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Transmitted Data (TD) Outgoing Data (from a DTE to a DCE)
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3
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Received Data (RD) Incoming Data (from a DCE to a DTE)
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4
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Request To Send (RTS) Outgoing flow control signal controlled by
DTE
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5
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Clear To Send (CTS) Incoming flow control signal controlled by
DCE
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6
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Data Set Ready (DSR) Incoming handshaking signal controlled by
DCE
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7
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Signal Ground Common reference voltage
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8
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Carrier Detect (CD) Incoming signal from a modem
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20
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Data Terminal Ready (DTR) Outgoing handshaking signal controlled
by DTE
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22
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Ring Indicator (RI) Incoming signal from a modem
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9 Pin Connector on a DTE device (PC connection)
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Male RS232 DB9
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Pin Number
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Direction of signal:
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1
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Carrier Detect (CD) (from DCE) Incoming signal from a modem
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2
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Received Data (RD) Incoming Data from a DCE
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3
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Transmitted Data (TD) Outgoing Data to a DCE
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4
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Data Terminal Ready (DTR) Outgoing handshaking signal
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5
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Signal Ground Common reference voltage
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6
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Data Set Ready (DSR) Incoming handshaking signal
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7
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Request To Send (RTS) Outgoing flow control signal
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8
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Clear To Send (CTS) Incoming flow control signal
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9
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Ring Indicator (RI) (from DCE) Incoming signal from a modem
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Null modem cables and Null modem adapters:
If you connect two DTE devices (or two DCE devices) using a straight
RS232 cable, then the transmit line on each device will be connected
to
the transmit line on the other device and the receive lines will likewise
be connected to each other. A Null Modem cable or Null Modem adapter
simply
crosses the receive and transmit lines so that transmit on one end is
connected to receive on the other end and vice versa. In addition to
transmit
and receive, DTR & DSR, as well as RTS & CTS are also crossed
in a Null Modem connection.
A Null Modem adapter is a small device that plugs in the line of a standard
serial cable that converts the connection to a Null Modem connection.
Null Modem adapters are available at most computer and office supply
stores for under $5.
Sartorius Cable Pinouts
Pinouts for other common types of cable
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