Full duplex means simultaneous bidirectional communications. Both sides send and receive with virtually no turnaround time.
On ASCII terminals used with the D3 System, full duplex is the mode in which characters entered from a keyboard are transmitted to the D3 host but not displayed to the screen. Normally, D3 ports are configured for full duplex also called echo-plex. Every character received is echoed to the terminal. Upon a keystroke, the character viewed on the screen has made a round trip from the system and back to the screen.
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