RS-232 cable: description, designation, technical characteristics

Strictly speaking, the RS-232 cable is the name of the standard that describes the interface of the connection from the computer to the data transfer device. RS - recommended standard, translated as "recommended standard", and 232 - type number. It was developed back in the 60s of last century. Today the new version of this standard, which was adopted in 1991 by the association of the telecommunications and electronics industries, is called EIA / TIA-232-E. However, most people continue to use the name "RS-232 cable", which is tightly "grown" to the interface.

The above interface allows the connection of the following devices: DTE (Data Terminal Equipment), and DCE (Data Communications Equipment). A PC is usually understood as a personal computer, and under the PDD is a modem. Although the RS-232 cable is also used to connect other peripherals (printer, mouse, etc.) to the PEUMS, as well as to connect to other computers or controllers. It is important to remember the designations DCE and DTE, as they are used in the names of interface signals and help to understand the description of the required implementation of the device.

Initially, the RS-232 cable had a 25-pin DB25 connector. The device type DTE was equipped with a socket-outlet ("mother"). Later, a "reduced" version of the interface with 9-pin DB9 connectors began to be used. This type of cable is common today.

Soldering the RS-232 cable

Below is the pin assignment of the 9-pin DB9 connector. The list shows the wiring connector ("dad") of data processing equipment, for example, a personal computer. The socket of the data transmission device is disconnected in such a way that both connectors are connected via a cable or directly "contact into contact".

1. Carrier Detect - the presence of carrier frequency.

2. Received Data - the received data.

3. Transmitted Data.

4. Data Terminal Ready - readiness of the DTE.

5. Signal Ground - common.

6. Data Set Read - readiness of the OPD.

7. Request To Send.

8. ClearToSend - ready to send.

9. Ring Indicator - the presence of a ring signal.

The data is transmitted over the RD and TD circuits. The remaining circuits are intended for displaying the status of DTR and DSR devices, controlling the transmission of CTS and RTS, as well as indicating the status of RI and CD lines. Only when an external modem is connected to a personal computer is a complete set of circuits used. When connecting other peripheral devices, such as controllers or mice, selective circuits are used that are necessary for a specific equipment. They depend on the software and hardware implementation of the device.

Description and technical parameters

The standard clearly defines the maximum possible length of the RS-232 cable - 15 meters with a data rate of 9600 bps. However, in practice it is checked that stable operation is achieved even with a longer wire length. It is believed that when using unshielded cable it is possible to increase the length to 30 meters, and when using a shielded cable it can be up to 75 meters. And this without loss of data transmission speed. If you reduce the speed by about half, the cable length is also doubled. It is recommended to use a cable based on twisted pair, in which case each signal wire is paired with a common wire. It is not recommended to combine the cable shield with the common signal.

You can often find an RS-232-USB cable. It is a standard interface, one end of which uses a USB connector.