Extended Functions - IBM 5150 Technical Reference

Break
The combination of the Ctrl and Break keys will result in the
keyboard routine signaling interrupt hex lA. Also the extended
characters (AL
=
hex 00, AH
=
hex 00) will be returned.
Pause
The combination of the Ctrl and Num Lock keys will cause the
keyboard interrupt routine to loop, waiting for any key except the
Num Lock key to be pressed. This provides a system- or
application-transparent method of temporarily suspending list,
print, and so on, and then resuming the operation. The
"unpause" key is thrown away. Pause is handled within the
keyboard routine.
Print Screen
The combination of the Shift and PrtSc (key 55) keys will result
in an interrupt invoking the print screen routine. This routine
works in the alphanumeric or graphics mode, with unrecognizable
characters printing as blanks.
Extended Functions
The keyboard routine does its own buffering. The keyboard
buffer is large enough that few typists will ever fill it. However, if
a key is pressed when the buffer is full, the key will be ignored
and the "bell" will sound.
Also, the keyboard routine suppresses the typematic action of the
following keys: Ctrl, Shift, Alt, Num Lock, Scroll Lock, Caps
Lock, and Ins.
System
BIOS 5-21