CentralNotice Software flow control From Wikipedia, the free encyclopedia Jump to: navigation , search "Xon" redirects here. For the Star Trek character, see Star Trek: Phase II § Lieutenant Xon . This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed. (March 2009) 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/XOFF flow control". This is in contrast to flow control via dedicated out-of-band signals — " hardware flow control " — such as RS...