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

118 Chapter5

Using Subsystem Break

Subsystem Break Summary

The following summarizes subsystem break processing and the

intrinsics involved:

1. A user written procedure must be provided to deﬁne how the

program should act upon receiving a subsystem break.

2. A call to XCONTRAP must be included in the program, specifying

the external address of the procedure written in Step 1 as the value

of plabel. This arms the

[CTRL]Y trap.

3. A call to FCONTROL(17) must be included in the program to enable

the subsystem break function.

4. If the subsystem break character is received during execution of the

program, the procedure speciﬁed in the call to XCONTRAP is

executed.

5. A call to RESETCONTROL must be executed when the program is

ready to receive another subsystem break.

6. A new subsystem break character may be deﬁned through

FCONTROL(41), if the terminal is placed in transparent mode, or

through FDEVICECONTROL.

7. You can redeﬁne your trap handling procedure at any point during

execution of the program through another call to XCONTRAP.

8. If desirable at any time, FCONTROL(16) may be called to disable

subsystem break. A call to FCONTROL(17) enables it again.