Serial Interfaces
A serial communications transceiver can use loopback for testing its functionality. For example, a device's transmit pin connected to its receive pin will result in the device receiving exactly what it transmits. Moving this looping connection to the remote end of a cable adds the cable to this test. Moving it to the far end of a modem link extends the test further. This is a common troubleshooting technique and is often combined with a specialized test device that sends specific patterns and counts any errors that come back (see Bit Error Rate Test). Some devices include built-in loopback capability.
A simple serial interface loopback test, called paperclip test, is sometimes used to identify serial ports of a computer and verify operation. It utilizes a terminal emulator application to send characters, with flow control set to off, to the serial port and receive the same back. For this purpose, a paperclip is used to short pin 2 to pin 3 (the receive and transmit pins) on a standard RS-232 interface using D-subminiature DE-9 or DB-25 connectors.
Read more about this topic: Loopback
Famous quotes containing the word serial:
“And the serial continues:
Pain, expiation, delight, more pain,
A frieze that lengthens continually, in the lucky way
Friezes do, and no plot is produced,
Nothing you could hang an identifying question on.”
—John Ashbery (b. 1927)