Asynchronous communication methods

This describes the two forms of asynchronous communication, one-way and two-way (which includes half-duplex and full-duplex).

Simplex, or one-way communication, is the simplest connection form between two devices. This mode of communication allows data to be transmitted in only one direction and requires only two lines be connected, for example, TxD (or RxD) and SG.

There are two forms of two-way communications: half-duplex and full-duplex. A connection in half-duplex mode allows data to be transmitted in two directions but not simultaneously. An analogy of half-duplex would be the use of a CB-radio where two-way communication is possible but only one person can speak at a time.

In full-duplex, or duplex mode, data communication can take place in two directions simultaneously. An analogy for full-duplex is a telephone conversation when both persons are talking at the same time.