Terminal Emulator is any hardware and/or software that allows a PC to operate as a terminal and connect to a back-end mainframe or terminal server. Terminal emulators can be designed to emulate specific terminal modes such as ANSI, VT52, VT100, VT220, TN3270, or TN5250.
Microsoft HyperTerminal, included with 32-bit Microsoft Windows operating systems, supports a variety of different terminal emulation modes.
Synchronous and Asynchronous terminals
In asynchronous terminals, data can flow in any direction at any time. In synchronous terminals a protocol controls who may send data when. IBM 3270-based terminals used with IBM mainframe computers are an example of synchronous terminals. They operate in an essentially “screen-at-a-time” mode. Users can make several changes to a page before submitting the updated screen to the remote machine as a single action.
Terminal emulators that simulate the 3270 protocol are available for most operating systems, for use both by those administering systems such as the z9, as well as those using the corresponding applications such as CICS.
Other examples of synchronous terminals include the IBM 5250, ICL 7561, Honeywell Bull VIP7800 and Hewlett-Packard 700/92.
The emulation mode on the clients must match the terminal mode running on the back-end system in order for communication to work. If you are trying to connect to an unknown mainframe or other back-end system and your emulator cannot automatically detect the terminal mode needed, try using ANSI mode first. If that fails, try VT100 and other popular terminal modes.