Configuring Systems for Terminals, Printers, and Other Serial Devices (32022-90057)

Describing Asynchronous Devices
How to Control Terminals
Chapter 9
176
Standard EOR Character
When users finish typing a line and press
[Return]
(the standard EOR character), data is
transmitted. The carriage return character terminates the read but it is not included in
the data of the read or counted in the number of actual characters read. When the EOR
character is detected, a carriage return is echoed to the screen and the ASC software
generates a line feed. This places the cursor at the beginning of the next line. The EOR
character can be replaced with another character during transparent editing; this is
done through the FCONTROL 41 intrinsic.
Additional EOR Character
Also referred to as an alternate EOR character, this character is included in the data and
the actual character count (byte count) of the data. The read does not end normally, but
terminates in an error stating that the additional EOR character was encountered. The
program that initiated the read must recover from the error by deleting the additional
EOR character from the input data, subtracting one from the byte count, and sending a
carriage return and line feed to place the cursor in its proper place.
AEOR characters can be defined through the FCONTROL 25 or, 40 intrinsics. Note that
when a read terminates, the program must call the FCHECK intrinsic to see why the read
terminated. If returns an error code of 31, it means the read ended with the additional
EOR character.
Up to 16 AEOR’s are available but only through the use of FDEVICECONTROL 192, 66.
System Console Attention Character
When
[CTRL]-A
is entered on the system console, it signals a
[CTRL]-A
console command.
The computer sends the system console a carriage return and line feed along with an
equals sign prompt (=), signaling that it is ready for the command.
[CTRL]-A
commands
are allowed only on the system console. For more information on the system console and
its special commands, refer to MPE/iX Managing Peripherals.
NOTE
[CTRL]-A
is not accepted as a special character from a terminal that is connected to a
DTC.
System Break
Using default operating conditions, the ASC software responds to a system break signal
from the terminal and alerts the computer. The system break function interrupts the
execution of programs, subsystems, and most MPE/iX commands. Once the program or
subsystem is interrupted, it can be aborted by entering the ABORT command or the
program or subsystem can be restarted by entering the RESUME command.
To transmit a system break signal, press
[Break]
. System break can be disabled
programmatically. Refer to the MPE/iX Intrinsics Reference Manual for more
information on system break.
Some application programs, such as block mode programs, change the settings of
terminals and the characteristics of their device files. These programs should return the
devices to normal operating mode before they complete.
If a program does not disable break (through the FCONTROL or FDEVICECONTROL
intrinsic), the user can still use
[Break]
. If
[Break]
is pressed, the program might not be
able to recover but the MPE/iX operating system will by assuming that the terminal is in
normal operating mode.