Automating Manufacturing Systems - Process Control and ...

plc serial - 27.7
DB-25
1 2 3 4 5 6 7 8 9 10 11 12 13
14 15 16 17 18 19 20 21 22 23 24 25
DB-9
1 2 3 4 5
6 7 8 9
Commonly used pins
1 - GND (chassis ground)
2 - TXD (transmit data)
3 - RXD (receive data)
4 - RTS (request to send)
5 - CTS (clear to send)
6 - DSR (data set ready)
7 - COM (common)
8 - DCD (Data Carrier Detect)
20 - DTR (data terminal ready)
Other pins
9 - Positive Voltage
10 - Negative Voltage
11 - not used
12 - Secondary Received Line Signal
Detector
13 - Secondary Clear to Send
14 - Secondary Transmitted Data
15 - Transmission Signal Element Timing
(DCE)
16 - Secondary Received Data
17 - Receiver Signal Element Timing
(DCE)
18 - not used
19 - Secondary Request to Send
21 - Signal Quality Detector
22 - Ring Indicator (RI)
1 - DCD
2 - RXD
3 - TXD
4 - DTR
5 - COM
6 - DSR
7 - RTS
8 - CTS
9 - RI
Note: these connectors
often have
very small numbers
printed on
them to help you
identify the pins.
Figure 27.5
Typical RS-232 Pin Assignments and Names
The handshaking lines are to be used to detect the status of the sender and receiver,
and to regulate the flow of data. It would be unusual for most of these pins to be connected
in any one application. The most common pins are provided on the DB-9 connector, and
are also described below.
TXD/RXD - (transmit data, receive data) - data lines
DCD - (data carrier detect) - this indicates when a remote device is present
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