Figure 2 -23. Sample Message Sequence
Control Mode. The line control is set in control
mode: when it receives or transmits the
ter; if the Disable command is executed; or if the
2702/03 is reset. The line is in control mode when
polling or addressing.
Text-Out Mode. The line control is set in text-out
mode when a
character is transmitted while the
line is in control mode or text-in mode. The line
remains in text-out mode until one of the conditions
that sets control mode occurs.
"Control Mode" item.)
Text-In Mode. The line control is set in text-in
mode when a
character is received from the
communications channel while the line is in control
The line remains in text-in mode until one
of the conditions that sets control mode occurs, or
This sets text-out mode.
(See preceding "Control Mode" and "Text-Out Mode"
Immediately following the issuance of the Read com-
mand when the line control is in control mode, the
normal 28-second line timeout is pre-empted by a
3-second short timeout. Once the first character
is received, the timeout period between characters
reverts to 28 seconds during Read command execution.
IBM TELEGRAPH LINE ADAPTER--OPERATIONS
The IBM Telegraph Line Adapter operations are the
same as those for the IBM Terminal Control Type I
except that the operations are altered to work with
telegraph lines. The operation codes and special
characters are also the same, except that the IBM
Telegraph Adapter does not use the Dial command.
Transmission-Code Error Detection Employed
The IBM Telegraph Line Adapter employs longitud-
inal redundancy checking (LRC) and vertical redun-
dancy checking (VR C).
The IBM Telegraph Line Adapter operates
similarly to the IBM Terminal Control Type I regard-
ing IBM 1050 operation, with an added provision for
equipment-implemented echo checking. When an Echo
Qheck signal is detected, the Unit Check status bit
and the Data Check sense bit are set. The command
being executed is not ended because of the occurrence
of an Echo Check.