Serial Port Cables
A serial port allows a computer to send data over long distances by converting parallel data to serial data. Typical computers will have one or two serial ports, usually designated as COM1 and COM2. The "standard" port is a 9-pin male connector on the computer, shown in Figure 12.9. (There are also 25-pin cables available.)
Figure 12.9 Standard 9-pin D connector
The following table describes the pin connection for the 9-pin and 25-pin serial cable connectors.
| 9-pin | 25-pin | Name | ID | Function |
|---|---|---|---|---|
| 1 | Shield | |||
| 3 | 2 | Transmitted Data | TX | Data sent from computer. |
| 2 | 3 | Receive Data | RX | Data sent to computer. |
| 7 | 4 | Request to Send | RTS | Computer is ready to send. |
| 8 | 5 | Clear to Send | CTS | "Other end" is ready to receive |
| 6 | 6 | Data Set Ready | DSR | "Other end" is ready to receive. |
| 5 | 7 | Signal Ground | SG | GND. |
| 1 | 8 | Data Carrier Detected | DCD | The modem has detected a signal from another modem. |
| 4 | 20 | Data Terminal Ready | DTR | Computer is ready to send. |
| 9 | 22 | Ring Indicator | RI | Modem detects line ringing. |