TTLINK  (Program)

TTLINK is a program that lets you interact with another computer over an
assigned DEC-20 TTY line.

TTLINK is useful with autodialers, hardwired EIA/RS-232 serial connections
between processors, and any other arrangement whereby you can assign a DEC-20
TTY port that is connected in some way as a terminal to another system.
Once the connection is established, all characters are passed through to the
remote host until you type the escape character, at which time TTLINK treats
the next character you type as a special command, the most important of which
is "C", which gets you back to the local DEC-20.


*  Form:

	ttlink
   or
	ttlink connect line /switches


*  Commands:

CONNECT line /switches	
		LINE is an octal TTY line number;  optional SWITCHES are:
			
	/DUPLEX:dup	Set to FULL if the remote host echos, or HALF if it
			does not.  The initial default is FULL.

	/PARITY:par	PAR can be one of NONE, MARK, EVEN, ODD, or SPACE.
			Parity initially defaults to NONE.


	/LOGFILE:name	Keep a transcript of the remote session in file NAME.

	/ESCAPE:n	Set the escape character; the default character is
			CTRL-Y (octal 31).  N is the octal value of an ASCII
			control character to be used as the escape character:
			for example, 1=CTRL-A, 32=CTRL-Z.  The escape character
			is used in conjunction with certain other commands: see
			the Single Character Commands section below.

	/SPEED:n	Tell TTLINK the speed of the port, and enable BREAK
			simulation (see below).  The speed is the baud rate,
			typically 300, 1200, 1800, 2400, 4800, or 9600.

	/BREAK-NULLS:n	For adjusting BREAK simulation (see below).
	

EXIT		Exit from TTLINK.  If you CONTINUE TTLINK, the duplex, parity,
		and escape character settings remain the same.

HELP		Print a help message.

STATUS		Display the current line number, duplex, escape character,
		parity, and logfile.


*  Single Character Commands:

While connected to the remote system, you may regain the attention of the local
TTLINK program by typing the escape character (CTRL-Y unless you define it
otherwise).  TTLINK waits for you to type another character, one of the
following:

?	Print a quick list of available escape commands.

C	Close the connection, return to the DEC-20.  You can resume the
	connection with another CONNECT command, or by continuing TTLINK.

P	PUSH to a new Exec.  Return via the POP command.

Q	Quit logging.

R	Resume logging.

S	Show status of connection: line, escape character, duplex, parity, and
	logfile.

B	Send a simulated BREAK signal (see below).

CTRL-Y	Typing the escape character twice in a row sends the escape character 
	to the remote host.

Initial defaults for CONNECT are FULL DUPLEX, escape character = CTRL-Y, PARITY
NONE, and no logging.  There are no initial defaults for line or logfile.
Defaults for subsequent CONNECT commands become whatever was specified in the
most recent CONNECT command.

All settings are established in the CONNECT command.  Command line arguments
(ccl, rescan) are accepted.  Thus, TTLINK is easily started from another
program with an RSCAN argument, and the superior can be in control of what
the settings are.


* Sending a BREAK signal from the DEC-20:

Sending a BREAK signal to the remote host can be a tricky business, because the
DEC-20 supplies no function to do this.  Therefore, TTLINK simulates a BREAK by
temporarily setting the speed of the line to 50 baud, sending several null
(ASCII 0) characters, and then setting the speed back to what it was.  But
TTLINK has no way of knowing wath the speed was unless you tell it, because
TOPS-20 does not remember the speed of a remote (modem-control) line.
Therefore, if you intend to send a BREAK signal to the remote host, you must
first use the following switch on the CONNECT command:

 /SPEED:n   The argument is a decimal number which is the current
	    speed of the line, such as 300 or 1200.

If you omit this switch, TTLINK will not try to send a BREAK.

You may transmit a BREAK by typing the BREAK key on your terminal ONLY IF YOU
ARE DIRECTLY CONNECTED TO THE SYSTEM WHICH IS RUNNING TTLINK (if your are
connected through a network, the BREAK generated by your terminal will not get
through to TTLINK).  In any case, you can always tell TTLINK to send a BREAK by
typing your escape character followed by the letter B.

If you find that your BREAK signal is not recognized correctly on the remote
system, you may have to adjust the number of NULL characters that are sent; the
following CONNECT command switch allows you to do this.

 /BREAK-NULLS:n

The default number of NULLs transmitted is 3.  If that is not enough, the
remote system may not react.  If that number is too high, the remote system may
sense two or more BREAKs.

[End of TTLINK.HLP 17-Nov-83]
