Serial port pinout usage

A ‘serial connection’ is a term used in the telecommunications field that refers to a method of sending data one bit at a time over a computer bus or communication line. Null modem cables are used to create a direct connection between two serial devices, negating the need for a modem or other communication equipment.

Serial communication is the standard method for data transfers in networked computers as well as long-distance connections. Parallel connections are used less commonly as the cables are more expensive and there can be synchronization issues that can lead to transmission inefficiencies.

Serial cables are used to connect serial devices through their COM ports. Varying types of serial ports require different serial connectors to operate correctly.

Learn more about the difference between a null modem and straight through serial cable in our special guide.

Virtual COM Port Driver is a professional-grade software tool that enables the user to set custom serial port pinouts. This affords great flexibility to serial communication system developers. Management of signal line pinouts can be accomplished by employing custom COM port pinout presets or relying on the standard pinout configuration.

Virtual COM Port Driver

Three options are available for setting signal lines pinout:

  • Standard enforces the default db9 serial port pinout for serial communications with partial handshaking.

    Standard RS-232 null modem pinout preset scheme:
  • Standard pinout
  • Loopback Mode allows communication between virtual COM ports using RS232 loopback handshaking.

    Loopback mode pinout preset scheme:
  • Loopback Mode
  • Custom serial connector pinout presets can be implemented and saved for later use in the tool’s software settings.

To set Custom serial connector pinout:

  1. Navigate to the ’Custom pinout’ tab.
  2. Choose the pair of virtual COM ports you want to work with in the Serial Ports Explorer.
  3. Simply check the boxes to connect the ‘IN’ and ‘OUT’ lines of your virtual COM port pair.
  4. Save your custom presets by naming it and clicking the ’Save preset’ button.

Serial communications require the use of two distinct types of devices. Data Terminal Equipment (DTE) is usually a computer that controls a serial connection and fits a male serial port connector. The DTE works in conjunction with a piece of Data Circuit-terminating Equipment (DCE) such as a modem that has a female COM port connector.

Signal lines are usually used to send data using the RS-232 protocol. These signals have the following meanings:

RTS (Request to Send) – a data exchange request that indicates data is ready to be send to the DTE.

CTS (Clear to Send) – here a positive voltage signal declares that a modem or DCE device is ready to receive data and the DTE can begin the data transmission.

DTR (DTE Ready) – this signal is sent from the DTE to a DCE device such as a modem. It is an indication that a connection can be initiated through the serial port controller (UART).

DSR (DCE Ready) – a modem sends a DSR signal to alert the computer that is is powered on, initialized, and ready for communications to begin.

DCD (Data Carrier Detect) – this signal between a DCE and DTE shows that there is a connection with the DCE and a distant modem. Active communication is indicated by logic ‘0’.

RI (Ring Indicator) – this signal simply informs a computer that a ringing signal from a telephone line is being received by the modem or DCE device.

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