TN3270(1)

NAME
tn3270 - full-screen remote login to IBM VM/CMS

SYNOPSIS
tn3270 sysname

DESCRIPTION
Tn3270 permits a full-screen, full-duplex connection from a VAX UNIX machine to an IBM machine running VM/CMS giving the appearance of being logged in directly to the remote machine on an IBM 3270 terminal. Of course you must have an account on the machine to which you wish to connect in order to log in. Tn3270 looks to the user in many respects like the Yale ASCII Terminal Communication System II. Tn3270 is actually a modification of the Arpanet TELNET user interface (see telnet(1)) that interprets and generates raw 3270 control streams.

Emulation of the 3270 terminal is done in the Unix process. This emulation involves mapping 3270-style commands from the host into appropriate sequences to control the user's terminal screen. Tn3270 uses curses(3x) and the /etc/termcap file to do this. The emulation also involves simulating the special 3270 keyboard keys (program function keys, etc.) by mapping sequences of keystrokes from the ASCII keyboard into appropriate 3270 control strings. This mapping is terminal dependent and is specified in a description file, /usr/share/misc/map3270, (see map3270(5)) or in an environment variable MAP3270 (see mset(1)). Any special function keys on the ASCII keyboard are used whenever possible. If an entry for the user's terminal is not found, tn3270 looks for an entry for the terminal type unknown. If this is not found, tn3270 uses a default keyboard mapping (see map3270(5)).

The first character of each special keyboard mapping sequence is either an ASCII escape (ESC), a control character, or an ASCII delete (DEL). If the user types an unrecognized function key sequence, tn3270 sends an ASCII bell (BEL), or a visual bell if defined in the user's termcap entry, to the user's terminal and nothing is sent to the IBM host.

If tn3270 is invoked without specifying a remote host system name, it enters local command mode, indicated by the prompt ``tn3270>''. In this mode, tn3270 accepts and executes the following commands:

	open	connect to a remote host
	close	close the current connection
	quit	exit tn3270
	z	suspend tn3270
	status	print connection status
	?	print help information

Other common telnet commands are not available in tn3270. Tn3270 command mode may also be entered, after connecting to a host, by typing a special escape character (typically control-C).

While in command mode, any host login session is still alive but temporarily suspended. The host login session may be resumed by entering an empty line (press the RETURN key) in response to the command prompt. A session may be terminated by logging off the foreign host, or by typing ``quit'' or ``close'' while in local command mode.

FILES
/etc/termcap
/usr/share/misc/map3270

AUTHOR
Greg Minshall

SEE ALSO
mset(1), telnet(1), termcap(3x), termcap(5), map3270(5), Yale ASCII Terminal Communication System II Program Description/Operator's Manual (IBM SB30-1911)

BUGS
Performance is slow and uses system resources prodigiously.

Not all 3270 functions are supported, nor all Yale enhancements.