TN3270 Server Manual

ITI Communication Protocol
TN3270 Server Manual—424097-001
6-2
Message Formats
Message Formats
The ITI protocol, as shown in Figure 6-1, takes an output buffer containing text to be
written and adds the following information before the existing text:
1. A command character (CMD)
2. A write control character (WCC)
3. Appropriate 3270 screen orders
The text line is following by:
1. An IS-A-COMMAND (IAC) character
2. An end-of-record (EOR) character
ITI Considerations
The following considerations apply to running the Guardian TN3270 Server in ITI
mode:
•
PA1 simulates the Break key of a conversational terminal. A system BREAK
message (-20) is sent to the application that owns the break. When an application
has taken ownership of the break, the terminal keyboard is unlocked immediately
upon receipt of input. If the break is unowned, the keyboard remains locked until the
next application READ or WRITEREAD procedure.
•
PA2 simulates the Ctrl-Y (EOF) key of a conversational terminal. File system
Error 1 (FEEOF) is returned to the application.
•
Function keys are not returned to conversational applications, such as TACL or
PERUSE.
•
The FC command (fix) works normally. Lines more than 80 characters long are
displayed in two parts, with a space between the two parts. When you use the FC
command to modify the second part of the line, move the cursor one extra character
position to the left.
Figure 6-1. ITI Protocol Message Format
Write Count
Sent to the
Terminal
Controller
E
O
R
I
A
C
Text Line to
be Written
3270
Screen
Orders
W
C
C
C
M
D
Passed by the
Application
3270
Specific
Telnet
Specific
001CDT .CDD