IBM XT 5160 Technical Reference page 137

Special Handling
System Reset
The combination of any Alt, Ctrl, and Del keys results in the
keyboard routine that starts a system reset or restart. System
reset is handled by BIOS.
Break
The combination of the Ctrl and Pause/Break keys results in the
keyboard routine signaling interrupt hex lB. The extended
characters AL=hex 00, and AH=hex 00 are also returned.
Pause
The Pause key causes the keyboard interrupt routine to loop,
waiting for any character or function key to be pressed. This
provides a method of temporarily suspending an operation, such
as listing or printing, and then resuming the operation. The
method is not apparent to either the system or the application
program. The key stroke used to resume operation is discarded.
Pause is handled internal to the keyboard routine.
Print Screen
The Print Screen key results in an interrupt invoking the
print-screen routine. This routine works in the alphameric or
graphics mode, with unrecognizable characters printing as blanks.
System Request
When the System Request (Alt and Print Screen) key is pressed, a
hex 8500 is placed in AX, and an interrupt hex 15 is executed.
When the Sys Req key is released, a hex 8501 is placed in AX,
and another interrupt hex 15 is executed. If an application is to
use System Request, the following rules must be observed:
4-42 lOl/102-Key Keyboard