Null Modem - Pin Mapping

Pin Mapping

This is one very common mapping which will work with software that relies on proper assertion of the CD signal.

Signal Name and Abbreviation DB-25 Pin DE-9 Pin Direction DE-9 Pin DB-25 Pin Signal Name Abbreviation
Frame Ground (chassis) FG 1 1 FG
Transmitted Data (TD) TxD 2 3 2 3 RxD
Received Data (RD) RxD 3 2 3 2 TxD
Request To Send RTS 4 7 8 5 CTS
Clear To Send CTS 5 8 7 4 RTS
Signal Ground SG 7 5 5 7 SG
Data Set Ready DSR 6 6 4 20 DTR
Data Carrier Detect (CD) DCD 8 1
Data Terminal Ready DTR 20 4 1 8 DCD
6 6 DSR

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