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Software flow control is a method of flow control used in computer data links, especially RS-232 serial. It uses special codes, transmitted in-band, over the primary communications channel. These codes are generally called XOFF and XON (from "transmit off" and "transmit on", respectively). Thus, "software flow control" is sometimes called "XON ...
Serial port. A male D-subminiature connector used for an RS-232 serial port on an IBM PC compatible computer along with the serial port symbol. A serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. [1] This is in contrast to a parallel port, which communicates multiple ...
Flow control (data) Not to be confused with Control flow. In data communications, flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from overwhelming a slow receiver. Flow control should be distinguished from congestion control, which is used for controlling the flow of data when ...
Universal asynchronous receiver-transmitter. A universal asynchronous receiver-transmitter (UART / ˈjuːɑːrt /) is a peripheral device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significant to the most significant, framed by start and ...
XMODEM is a simple file transfer protocol developed as a quick hack by Ward Christensen for use in his 1977 MODEM.ASM terminal program. It allowed users to transmit files between their computers when both sides used MODEM. Keith Petersen made a minor update to always turn on "quiet mode", and called the result XMODEM.
If either of these two octets appears in the transmitted data, an escape octet is sent, followed by the original data octet with bit 5 inverted. For example, the byte 0x7E would be transmitted as 0x7D 0x5E ("10111110 01111010"). Other reserved octet values (such as XON or XOFF) can be escaped in the same way if necessary.
The Flow Control specification defines packet formats and protocols for simple XON/XOFF flow control operations. Flow control packets can be originated by switches and endpoints. Reception of a XOFF flow control packet halts transmission of a flow or flows until an XON flow control packet is received or a timeout occurs.
Digital Equipment Corporation invented a convention which used 19 (the device control 3 character , also known as control-S, or XOFF) to "S"top transmission, and 17 (the device control 1 character , a.k.a. control-Q, or XON) to start transmission. It has become so widely used that most don't realize it is not part of official ASCII.