Vectors With Special Meanings - IBM 5150 Technical Reference

Vectors with Special Meanings
Interrupt Hex 1 B - Keyboard Break Address
This vector points to the code to be used when the Ctrl and Break
keys are pressed on the keyboard. The vector is invoked while
responding to the keyboard interrupt, and control should be
returned through an IRET instruction. The power-on routines
initialize this vector 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. Also, all I/O devices should be
reset in case an operation was underway at that time.
Interrupt Hex 1 C - Timer Tick
This vector points to the code to be executed on 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.
It
is the responsibility of the
application to save and restore all registers that will be modified.
Interrupt Hex 1 D - Video Parameters
This vector points to a data region containing the parameters
required for the initialization of the 6845 on the video card. Note
that there are four separate tables, and all four must be
reproduced if all modes of operation are to be supported. The
power-on routines initialize this vector to point to the parameters
contained in the ROM video routines.
~
5-6
System
BIOS