XON (Transmission On) is a control character in telecommunications and computer networking used to signal that the transmission of data can continue. It is part of the XON/XOFF software flow control method, which is employed especially in serial communications.
Here’s a brief overview of XON:
Control Character: XON is represented by the control character with the ASCII value of 17 (or 0x11 in hexadecimal). In ASCII representation, it’s denoted as ^Q or Ctrl-Q.
Function: When the receiving device sends an XON character to the transmitting device, it signals that it’s ready to receive more data. Essentially, it tells the transmitting device, “I’m ready; you can send data now.”
Usage: XON is primarily used in conjunction with the XOFF character in the XON/XOFF flow control scheme.
- When the receiving device’s buffer (temporary storage) is nearing its capacity and can’t handle more incoming data immediately, it sends an XOFF (Transmission Off) signal to the transmitting device to pause data transmission.
- When the receiving device has processed some of its buffer and is ready to receive more data, it sends an XON signal to the transmitting device to resume the data flow.
Software Flow Control: XON/XOFF is a software-based flow control mechanism. This means it relies on these control characters embedded within the data stream itself, rather than on separate hardware signals or lines, to manage data transmission.
Advantages: The main advantage of using XON/XOFF is that it doesn’t require any additional hardware or dedicated signal lines, making it suitable for simple serial connections.
Drawbacks: One potential issue with XON/XOFF is the chance of data confusion if the actual transmitted data contains XON or XOFF characters. This can be managed using various techniques, such as data escaping or byte stuffing.
In essence, XON is a control signal that says, “It’s okay to send more data,” and is integral to the software-based flow control method known as XON/XOFF.