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

Chapter 5 115
Using Subsystem Break
Subsystem Break Intrinsics
Figure 5-1 Illustrating a Subsystem Break Handler
The procedure illustrated by Figure 5-2 shows the other half of what
you must do to provide subsystem break capabilities in a program. This
procedure sets up and enables subsystem break.
The procedure first calls XCONTRAP, which passes the address of the
[CTRL]Y procedure shown in Figure 5-1. This arms the [CTRL]Y trap
(enables the subsystem break handler). The Pascal/iX waddress
function is used to pass the address in this example.
The address of the break handler is passed in the plabel parameter of
the XCONTRAP intrinsic. The oldplabel parameter will return the
address of the old trap handler, if one was previously armed. If there
was no previous address, this parameter will return a 0.