Switched Network Control - Texas Instruments 990 User Manual

~-------
~
946289-9701
Table l·l. Data Link Control Characters (Continued)
Control Character
ETX
Description
Indicates the end of the last transmission block of a message.
. .
EOT
ENQ
ACKO/ I
NAK
OLE
WACK
RVI
TTD
lndieat~s the end of a transmission.
Indicates that the station sending the ENQ has data to transmit.
Indicates the receiving station has received the transmitted block of
data successfully.
Indicates the receiving station has received the transmitted block of
data unsuccessfully, i.e., the transmission had errors in it.
Combines with other characters to provide additional data link control
characters.
Indicates the receiving station has received the transmitted block of
data successfully and requests that the transmitting station temporarily
delay before its next transmission.
Indicates the receiving station has received the 'transmitted block,of
data successfully and requests that the transmitting station stop
transmitting so that the receiving station may transmit priority data.
Indicates the transmitting station has data to transmit. is temporarily
not ready to transmit it, but does not wish to give up the line.
2.2.4 SWITCHED NETWORK CONTROL.
As with the
IBM
3780 and 2780, the Emulator is
capable of automatic answer and disconnect when the line is attached to a switched (dial-up)
network and is equipped with an appropriate auto-answer modem.
The automatic answer and disconnect feature enables the Emulator to do the following:
• Automatically answer an incoming call without operator intervention.
• Receive and execute a disconnect command from a remote station (a OLE EQT sequence
is sent by the remote station).
•
Automatically disconnect when the connection is not active. The Emulator automatically
disconnects the connection after a 20-second timeout if no meaningful activity has
occurred. (This feature is selectable during installation.) If at any time during the timeout
meaningful activity takes place, the timeout restarts with a new 20-second time period. The
disconnection can be accomplished sooner through the use of the Disconnect (DISC)
command if desired.
• Cancel a transmission initiated from an input device if the transmission is initiated prior to
beginning the disconnect. This is accomplished by the transmitting station issuing an
ABORT COM command or physically breaking the connection, or by the modem sensing
a disconnect from the remote station after the transmission is initiated.
2-2
Digital Systems Group