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In a full-duplex system, both users can communicate at the same time. A telephone is the most common example of a full-duplex system because both users can speak and be heard at the same time on each end. Some types of full-duplexing methods are: Time-division duplex (TDD) Frequency-division duplex (FDD) Echo cancellation
Another commonly used notation represents the mode as a (CPOL, CPHA) tuple; e.g., the value '(0, 1)' would indicate CPOL=0 and CPHA=1. In Full Duplex operation, the main device could transmit and receive with different modes. For instance, it could transmit in Mode 0 and be receiving in Mode 1 at the same time.
For example, a walkie-talkie or a DECT phone or so-called TDD 4G or 5G phones requires only a single frequency for bidirectional communication, while a cell phone in the so-called FDD mode is a full-duplex device, and generally requires two frequencies to carry the two simultaneous voice channels, one in each direction.
Before signaling will work, the sender and receiver must agree on the signaling parameters: Full or half-duplex operationThe number of bits per character -- currently almost always 8-bit characters, but historically some transmitters have used a five-bit character code, six-bit character code, or a 7-bit ASCII.
This may happen, for example, if one is configured for autonegotiation while the other one has a fixed mode of operation that is full duplex (no autonegotiation). In such conditions, the autonegotiation device correctly detects the speed of operation but is unable to correctly detect the duplex mode.
Asynchronous response mode is an HDLC addition [1] for use over full-duplex links. While retaining the primary/secondary distinction, it allows the secondary to transmit at any time. Thus, there must be some other mechanism to ensure that multiple secondaries do not try to transmit at the same time (or only one secondary).
DF-1 / DF1 protocol is an asynchronous byte-oriented protocol that is used to communicate with most Allen Bradley RS-232 interface modules. DF1 protocol consists of link layer and application layer formats.
RS-485, like RS-422, can be made full-duplex by using four wires. [8] Since RS-485 is a multi-point specification, however, this is not necessary or desirable in many cases. RS-485 and RS-422 can interoperate with certain restrictions.