| PIN | SIGNAL | SIGNAL NAME | FLOW | DESCRIPTION |
|---|---|---|---|---|
| 4 22 |
SD or TD |
Transmit Data | Output | Data transmitted to the data communications equipment. |
| 6 24 |
RD | Receive Data | Input | Data received from the data communications equipment. |
| 7 25 |
RS or RTS |
Request to Send | Output | Signal sent to the data communications equipment, asking if it is ready to start accepting data. |
| 9 27 |
CS or CTS |
Clear to Send | Input | Ready to accept data signal from the data communications equipment. |
| 11 29 |
DM or DSR |
Data Set Ready | Input | Data communications equipment indicates the status of the local data set. |
| 19 | SG | Signal Ground | None | Signal Ground provides a reference level for the signal voltages. |
| 13 31 |
RR or DCD |
Data Carrier Detect | Input |
Data communications equipment detected "carrier." Example: a modem senses tones sent to it by another modem over phone lines. |
| 5 23 |
ST or TC |
Transmit Clock from DCE |
Input | Transmit clock from the modem. Usually not used for asynchronous devices (terminals, printers, and modems, etc.). |
| 8 26 |
RT or RC |
Receive Clock from DCE |
Input | Receive clock from the modem. Usually not used for asynchronous devices (terminals, printers, and modems, etc.). |
| 12 30 |
TR or DTR |
Data Terminal Ready |
Output | The DTE is powered on and ready to communicate as the "local data terminal" with the data communication equipment. For example, the modem. |
| 17 35 |
TT or TCO |
Transmit Clock from DTE |
Output | Provides transmit clock from the DTE. Usually not used for asynchronous devices (terminals, printers, and modems, etc.). |