| DTE Normally a Computer | Standard Male | Standard Female | DCE Normally a Device: Modem, Scale, Barcode Scanner, Etc | |||||||
| Direction | Signal Name | Mnemonic | DE-9 Pin | DE-9 Pin | Mnemonic | Signal Name | Direction | |||
| Input | <-- | Data Carrier Detect | DCD | 1 | 1 | DCD | Data Carrier Detect | <-- | Output | |
| Input | <-- | Receive Data | RD | 2 | 2 | RD | Receive Data | <-- | Output | |
| Output | --> | Transmit Data | TD | 3 | 3 | TD | Transmit Data | --> | Input | |
| Output | --> | Data Terminal Ready | DTR | 4 | 4 | DTR | Data Terminal Ready | --> | Input | |
| Signal Ground | <--> | Signal Ground | SG | 5 | 5 | SG | Signal Ground | <--> | Signal Ground | |
| Input | <-- | Data Set Ready | DSR | 6 | 6 | DSR | Data Set Ready | <-- | Output | |
| Output | --> | Request To Send | RTS | 7 | 7 | RTS | Request To Send | --> | Input | |
| Input | <-- | Clear To Send | CTS | 8 | 8 | CTS | Clear To Send | <-- | Output | |
| Input | <-- | Ring Indicator | RI | 9 | 9 | RI | Ring Indicator | <-- | Output |