The exchange of digital data between devices one character at a time and one character element, i.e., bit, at a time over a single circuit and channel. Serial communications can be in either asynchronous or synchronous mode. Serial, rather than parallel, communications are used exclusively in wireline transmission, except over extremely short distances, primarily due to the lower cost of provisioning a single circuit. A serial-input-parallel-output (SIPO) shift register is used to interface a serial circuit to a parallel circuit. See also asynchronous, channel, circuit, parallel communications, shift register, and synchronous.