X25AM Programming Manual

ITI Applications
X25AM Programming Manual—527201-001
2-7
The PACKET ASSEMBLER/ DISASSEMBLER
(PAD)
•
A Clear is received.
•
An Invitation to Clear is received and a Clear Request is sent.
•
The remote terminal modem is disconnected, deactivating the carrier signal.
When the circuit is disconnected, any outstanding READ and/or WRITE requests are
terminated by ITI, which returns error 140 (circuit disconnected) to the requester.
The PACKET ASSEMBLER/ DISASSEMBLER
(PAD)
The PAD is an essential component of the communication path between your
application and the terminal. The terminals supported by ITI are asynchronous. The
X.25 network requires packetized data. The PAD constructs packets from single
character data coming from the terminal and separates data in packets coming from
the network into single characters for the terminal.
A PAD can be a separate device connected to the terminal and the network or a part of
the network. Figure 2-3
on page 2-8 illustrates these two configurations.
Figure 2-2. The Packet Assembler/Disassembler
VST0202.vsd
X.25
Packet-Switched
Network
Data Packets
PAD
Host
A
B C
Characters