IBM 5170 Technical Reference page 162

When Caps Lock is pressed, it toggles the Caps Lock Mode
indicator. If the indicator was on, it will go off; and if it was off,
it will go on.
Scroll Lock: This key is interpreted by appropriate application
programs as indicating that the use of cursor control keys should
cause windowing over the text rather than cursor movement. ,..-...,
When the Scroll Lock key is pressed again, it reverses the action.
The keyboard routine simply records the current shift state of the
Scroll Lock key. It is the responsibility of the application
program to perform the function. When Scroll Lock is pressed, it
toggles the Scroll Lock Mode indicator. If the indicator was on, it
will go off; and if it was off, it will go on.
Num Lock: This key shifts keys 90-93 and 95-104 to upper
case. When Num Lock is pressed again, it reverses the action.
Num Lock is handled internal to the keyboard routine. When
Num Lock is pressed, it toggles the Num Lock Mode indicator. If
the indicator was on, it will go off; if it was off, it will go on.
Shift Key Priorities
and
Combinations: If combinations of the
Alt, Ctrl, and Shift keys are pressed and only one is valid, the
priority is as follows: the Alt key is first, the Ctrl key is second,
and the Shift key is third. The only valid combination
is
Alt and
Ctrl, which is used in the system-reset function.
SysReq
When the Sys key is pressed, a hex 8500 is placed in AX, and an
interrupt 15 is executed. When the Sys key is released, a hex
8501 is placed in AX, and another interrupt 15 is executed.
If
an
application is to use the Sys key, the following rules must be
observed:
Save the previous address
Overlay interrupt vector hex 15
Check AH for a value of hex 85
If yes, process may begin
5-20 System BIOS