IBM 5170 Technical Reference page 149

• Joystick support
• 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 will be executed when the Ctrl and Break keys are
pressed on the keyboard. The vector is invoked while responding
to 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.
Control may be retained by this routine with the following
problems:
• 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 IIO devices should be reset in case an operation was
underway at the same time.
Interrupt 1 C--Timer Tick: This vector points to the code that
will be executed at every system-dock 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.
System BIOS 5-7