Half duplex

A half duplex connection is a connection where transmission in both directions is possible, but not at the same time. Typical examples of a half duplex are a walkie-talkie and a mobile radio, where a button on the microphone has to be pushed to switch from listening to talking.

In radiocommunications, this kind of operation is also called simplex if both directions use the same frequency or semi duplex if they operate on different frequencies.