Data circuits | Control circuits | Voltage |
---|---|---|
0 (space) | Asserted | +3 to +15 V |
1 (mark) | Deasserted | −15 to −3 V |
Circuit | Direction | DB-25 pin | |||
---|---|---|---|---|---|
Name | Typical purpose | Abbreviation | DTE | DCE | |
Data Terminal Ready | DTE is ready to receive, initiate, or continue a call. | DTR | out | in | 20 |
Data Carrier Detect | DCE is receiving a carrier from a remote DCE. | DCD | in | out | 8 |
Data Set Ready | DCE is ready to receive and send data. | DSR | in | out | 6 |
Ring Indicator | DCE has detected an incoming ring signal on the telephone line. | RI | in | out | 22 |
Request To Send | DTE requests the DCE prepare to transmit data. | RTS | out | in | 4 |
Ready To Receive | DTE is ready to receive data from DCE. If in use, RTS is assumed to be always asserted. | RTR | out | in | 4 |
Clear To Send | DCE is ready to accept data from the DTE. | CTS | in | out | 5 |
Transmitted Data | Carries data from DTE to DCE. | TxD | out | in | 2 |
Received Data | Carries data from DCE to DTE. | RxD | in | out | 3 |
Common Ground | Zero voltage reference for all of the above. | GND | common | 7 | |
Protective Ground | Connected to chassis ground. | PG | common | 1 |
Signal | Pin |
---|---|
Common Ground | 7 (same as primary) |
Secondary Transmitted Data (STD) | 14 |
Secondary Received Data (SRD) | 16 |
Secondary Request To Send (SRTS) | 19 |
Secondary Clear To Send (SCTS) | 13 |
Secondary Carrier Detect (SDCD) | 12 |
Description | |
---|---|
Green | Monitored port is active (has initialized without error). |
Yellow | Monitored port is in loopback mode. |
Off | Monitored port is not active (has failed to initialize). |
Serial interface | 3 | Male serial cable |
Female serial cable |