RS-232 Pin Outs
- an overview RS232 pin outs or pinouts configurations used on the different
connector types including RS232 9pin and RS232 25 pin connectors.
To ensure that communications are possible between a variety
of RS232 devices it is necessary that standard RS232 pin outs are used. Although
a variety of connectors are used, the pin outs for each type of connector has to
be standardised so that it is possible to know how to connect to them, and to be
able to use standard RS232 cables.
The most common connectors use the D-type often also called a
sub-D connector and both 9 way and 25 way versions are used. In addition to this
other types of connector may be used on occasions.
When using RS232, two main types of equipment are nominated.
One is a data Terminal Equipment, DCE and the other is known as the Data
Terminal Equipment, DTE. These abbreviations are widely used within RS232 and
other communications terminology.
By using the pin outs as detailed below the RS232 cables used
should be a "one to one" configuration. This considerably simplifies the
manufacture of RS232 cables and often means that standard cables can be used.
RS232 25 pin connections and functions
The RS232 (EIA-232-A) specification provides a full set of details for a wide
variety of connections that can be used with RS232. While many of them are not
normally known, they may be used in some circumstances and therefore the details
are provided here for reference.
RS232 25 pin signal definition for
the DTE device - looking into the DTE connector
DTE device is often a PC.
|
| DTE Pin No |
Circuit name |
Abbreviation |
Source |
| 1 |
Protective earth |
|
|
| 2 |
Transmitted data |
TXD |
DTE |
| 3 |
Received data |
RXD |
DCE |
| 4 |
Request to send |
RTS |
DTE |
| 5 |
Clear to send |
CTS |
DCE |
| 6 |
Data set ready |
DSR |
DCE |
| 7 |
Signal ground |
|
|
| 8 |
Data carrier detect |
DCD |
DCE |
| 9 |
Reserved for data set test |
|
|
| 10 |
Reserved for data set test |
|
|
| 11 |
Unassigned |
|
|
| 12 |
Secondary received signal detector
|
|
DCE |
| 13 |
Secondary clear to send |
|
DCE |
| 14 |
Secondary transmitted data |
|
DTE |
| 15 |
Transmission signal element timing
|
|
DCE |
| 16 |
Secondary received data |
|
DCE |
| 17 |
Receive signal element timing |
|
DCE |
| 18 |
Unassigned |
|
|
| 19 |
Secondary request to send |
|
DTE |
| 20 |
Data terminal ready |
DTR |
DTE |
| 21 |
Signal quality detector |
|
DCE |
| 22 |
Ring indicator |
|
DCE |
| 23 |
Data signal rate selector |
|
DCE/DTR |
| 24 |
Transmit signal element timing |
|
DTE |
| 25 |
Unassigned |
|
|
RS232 25 pin signal definition for
the DCE device - looking into the DCE connector
DTE device is often a device such as a modem.
|
| DCE Pin No |
Circuit name |
Abbreviation |
Source |
| 1 |
Protective earth |
|
|
| 2 |
Received data |
RXD |
DCE |
| 3 |
Transmitted data |
TXD |
DTE |
| 4 |
Clear to send |
CTS |
DCE |
| 5 |
Request to send |
RTS |
DTE |
| 6 |
Data set ready |
|
DCE |
| 7 |
Signal ground |
|
|
| 8 |
Data carrier detect |
DCD |
DCE |
| 9 |
Reserved for data set test |
|
|
| 10 |
Reserved for data set test |
|
|
| 11 |
Unassigned |
|
|
| 12 |
Secondary received signal detector
|
|
DCE |
| 13 |
Secondary request to send |
|
DTE |
| 14 |
Secondary received data |
|
DCE |
| 15 |
Transmission signal element timing
|
|
DCE |
| 16 |
Secondary transmitted data |
|
DTE |
| 17 |
Receive signal element timing |
|
DCE |
| 18 |
Unassigned |
|
|
| 19 |
Secondary clear to send |
|
DCE |
| 20 |
Data terminal ready |
DTR |
DTE |
| 21 |
Signal quality detector |
|
DCE |
| 22 |
Ring indicator |
|
DCE |
| 23 |
Data signal rate selector |
|
DCE/DTR |
| 24 |
Transmit signal element timing |
|
DTE |
| 25 |
Unassigned |
|
|
By using these configurations it means that an RS232 cable
connecting a DTE to a DCE will be wired in a one-to-one configuration, i.e. pin
1 to pin 1, etc.
RS232 9pin connections, functions and pin-outs
Although the RS232 25 pin configuration with a 25 way D-type connector is very
widely used, in many applications the smaller 9 way D-type connector is used in
many applications. It provides an obvious size and cost benefit. Also the RS232
9pin configuration is quite sufficient in most circumstances because many of the
lines available for RS232 signalling are rarely used. This means that the 9 way
connector is able to provide all the required connectivity for most
applications.
RS232 9pin signal definition for the
DTE device - looking into the DTE connector
DTE RS232 device is often a PC.
|
| Pin No |
Circuit name |
Abbreviation |
Source |
| 1 |
Received line signal detect |
|
|
| 2 |
Receive data |
RXD |
|
| 3 |
Transmit data |
TXD |
|
| 4 |
Data terminal ready |
DTR |
|
| 5 |
Signal ground |
|
|
| 6 |
Data set ready |
DSR |
DCE |
| 7 |
Request to send |
RTS |
|
| 8 |
Clear to send |
CTS |
|
| 9 |
Ring indicator |
|
|
RS232 9pin signal definition for the
DCE device - looking into the DCE connector
DCE device is often a modem.
|
| Pin No |
Circuit name |
Abbreviation |
Source |
| 1 |
Received line signal detect |
|
|
| 2 |
Transmit data |
TXD |
|
| 3 |
Receive data |
RXD |
|
| 4 |
Data terminal ready |
DTR |
|
| 5 |
Signal ground |
|
|
| 6 |
Data set ready |
DSR |
DCE |
| 7 |
Clear to send |
CTS |
|
| 8 |
Request to send |
RTS |
|
| 9 |
Ring indicator |
|
|
By using these configurations it means that an RS232 cable
connecting two RS232 devices, i.e. a DTE to a DCE will be wired in a one-to-one
configuration, i.e. pin 1 to pin 1, etc.
RS232 Pin Out Summary
RS232 is still widely used throughout the electronics and telecommunications
industries. When using this form of serial communications system it is essential
to ensure that the correct connections are being used. Accordingly it is
necessary to check the RS232 pin outs when making any leads or other
connections. Both RS232 25 pin and RS232 9pin connectors are used when making
connections, so checking the correct connector and pin connections is important
to ensure that communications can take place.
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