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Standard Rj45 To Db25 Pinout Assignments

EIA/TIA-561 Pin Layout (serial interface via 8-pin connector)

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Here a useful pinout for anyone who wants to connect their PC to devices such as key or PBX (Private Branch eXchange)  phone system or other devices that have a serial port connected to a 8P8C jack. In fact, phone systems may have more than one port of this kind. For example, Avaya Partner ACS and Avaya Merlin Magix have two ports with this pin layout - the Admin port and the SMDR port.
Please note that there are several competing pinouts for this kind of connection. For example, Cisco console adapter has different pin layout even though it is also a DB9-to-8-pin connector device.
EIA/TIA-561 Pin Layout Diagram with DB9 connector

The EIA/TIA-561 standard itself only applies to the 8P8C end of such cable. Therefore, we also provide the DB25 pinout in case your PC has a DB25 serial port available. Please see the pin assignment table below for DB25-to-DB9 conversion

EIA/TIA-561 Pin Layout Diagram with DB25 connector


EIA/TIA-561 Pin Layout and RS-232 pin assignments
8P8C (RJ45)DB9DB25SignalDescription
1922RIRing Indicator
218DCDData Carrier Detect
3420DTRData Terminal Ready
457SGSignal Ground
523RXDReceived Data
632TXDTransmitted Data
785CTSClear To Send
874RTSRequest To Send

RS232 pinout

RS232 pinout standards exist for both DB9 and DB25 connectors as shown below:

1Protective Ground
2TXD3Transmitted Data
3RXD2Received Data
4RTS7Request To Send
5CTS8Clear To Send
6DSR6Data Set Ready
7GND5Signal Ground
8CD1Received Line Signal Detector
9Reserved for data set testing
10Reserved for data set testing
12SCFSecndry Rcvd Line Signl Detctr
13SCBSecondary Clear to Send
14SBASecondary Transmitted Data
15DBTransmisn Signal Timng
16SBBSecondary Received Data
17DDReceiver Signal Element Timing
19SCASecondary Request to Send
20DTR4Data Terminal Ready
21CGSignal Quality Detector
229Ring Indicator
23CH/CIData Signal Rate Selector
24DATransmit Signal Element Timing

Location of Pin 1 on DB connector

RS422 and RS485 DB9 pinout