Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

Chapter 8 173
Intrinsics Reference
FCONTROL(14, 15)
FCONTROL(14, 15)
Parameters
controlcode 14 — Disables the system break function.
15 — Enables the system break function.
param 16-bit unsigned integer by reference
(required)
This parameter has no meaning for these controlcode
values. Enter a dummy value of 0 to satisfy the internal
requirements of the intrinsic.
Notes A call to FCONTROL with a controlcode value of 14
or 15 determines whether or not a terminal will react to
a system break request. Use 14 to disable system
break, 15 to enable system break.
System break is enabled by default for any terminal on
which a session is active. Any time a user presses the
[Break] key (or the CAUSEBREAK intrinsic is called),
MPE/iX will attempt to interrupt processing and place
the terminal at the Command Interpreter level
(: prompt). Many MPE/iX commands are breakable, as
are program commands that invoke subsystems or run
user programs.
When system break is enabled and a system break is
received, EOR, read timer, terminal mode and echo
values are saved by the DTS software, so that they can
be restored when normal processing is resumed. If
system break is entered during processing of a
character mode read or write, data is lost. Any read
that is interrupted by a break will be reissued by the
system after a Resume command is typed.
Some application programs change the settings of
terminals and/or the characteristics of their devicefiles.
In such cases it may be undesirable to allow system
break processing to occur. For example, you should
disable system break when using block mode. Doing so
will prevent data loss or corruption that could occur
should the
[Break] key be pressed during a block mode
read. It also avoids problems that can occur because
your program is unable to return the device to normal
operating mode if system break is entered.