IBM AT 5170 Technical Reference page 179

•
System Request key pressed
•
Wait
•
Move block
~
• Extended memory size determination
•
Processor to protected mode
Additional information about these functions may be found in the
BIOS listing.
Interrupt IB-Keyboard Break Address:
This vector points to
the code that is executed when the Ctrl and Break keys are
pressed. The vector is invoked while responding to a keyboard
interrupt, and control should be returned through an IRET
instruction. The power-on routines initialize this vector to point
to an IRET instruction so that nothing
will
occur when the Ctrl
and Break keys are pressed unless the application program sets a
different value.
,-...., This routine may retain control with the following considerations:
• The Break may have occurred during interrupt processing, so
that one or more End of Interrupt commands must be sent to
the 8259 controller.
• All
II
0 devices should be reset in case an operation was
underway at the same time.
Interrupt I C-Timer Tick:
This vector points to the code that
will be executed at every system-clock tick. This vector is
invoked while responding to the timer interrupt, and control
should be returned through an IRET instruction. The power-on
routines initialize this vector to point to an IRET instruction, so
that nothing will occur unless the application modifies the pointer.
The application must save and restore all registers that will be
modified.
Interrupt ID-Video Parameters:
This vector points to a data
region containing the parameters required for the initialization of
the 6845 on the video adapter. Notice that there are four
System BIOS 5-7