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Signals
The following table lists commonly used RS-232 signals and pin assignments.[8] See serial port (pinouts)for non-standard variations including the popular DE-9connector.
Signal | Origin | DB-25pin | |||
Name | Typical purpose | Abbreviation | DTE | DCE | |
Indicates presence of DTE to DCE. | DTR | ● | 20 | ||
DCE is connected to the telephone line. | DCD | ● | 8 | ||
Data Set Ready | DCE is ready to receive commands or data. | DSR | ● | 6 | |
Ring Indicator | DCE has detected an incoming ring signal on the telephone line. | RI | ● | 22 | |
Request To Send | DTE requests the DCE prepare to receive data. | RTS | ● | 4 | |
Clear To Send | Indicates DCE is ready to accept data. | CTS | ● | 5 | |
Transmitted Data | Carries data from DTE to DCE. | TxD | ● | 2 | |
Received Data | Carries data from DCE to DTE. | RxD | ● | 3 | |
Common Ground | GND | common | 7 | ||
Protective Ground | PG | common | 1 |
The signals are named from the standpoint of the DTE. The ground signal is a common returnfor the other connections. The DB-25 connector includes a second "protective ground" on pin 1.