X25AM Programming Manual

ITI Applications
X25AM Programming Manual—527201-001
2-6
Clearing a Call
WRITE Request
Clearing a Call
Clearing a call can be initiated by the application, the terminal user, the operator, or the
network.
Application
The application clears a call when it performs the last CLOSE (there are no more
OPENs). ITI sends a Clear Request.
The application requests a Call cleared when it issues a CONTROL 12. ITI then sends
an Invitation to Clear.
A Clear Request can overtake the WRITE data and arrive before it. For that reason, a
CONTROL 12 (Invitation to Clear) should always be used after a WRITE to prevent
data loss. An Invitation to Clear packet is a form of data packet, which cannot overtake
the WRITE data.
After the remote device or application receives an Invitation to Clear packet it then
issues a Clear Request to initiate clearing the call. Upon receipt of a Clear Indication,
the response is a Clear Confirmation.
Terminal
The terminal user clears a call when Escape From Data Transfer is enabled, allowing
the terminal to send a DLE character to the PAD (so that it is in command mode)
followed by a CLR command. The PAD sends a Clear request to the host DTE. If a
Clear Confirmation is returned, the PAD returns CLR CONFirm to the terminal.
Operator
The operator clears a call when an ABORT is issued with SCF.
Network
A call is cleared when:
•
There is a network interface problem resulting in a packet level Restart or frame
level Disconnect.
CONVERSATION MODE. With a WRITE request, conversation mode is used
to send control and escape sequences to the
terminal. WRITE is not used if a reply is expected.
PAGE MODE. With a WRITE request, page mode is used to send
control and escape sequences to the terminal, to
transmit screens (or partial screens) of information to
the terminal, and to unlock the terminal keyboard.
WRITE is not used if a reply is expected.