The Interrupts; Summary - Husky MP2500 Manual

19. The Interrupts

This chapter briefly describes the interrupts used on MP2500. The BIOS
interrupts are described in detail in Chapters 20 to 30. The hardware
interrupts are described in section 31.3. The MS-DOS interrupts are
described in the MS-DOS Programmer's Manual.

19.1 Summary

The Intel i386ex microprocessor supports 256 different interrupts. There are
three types:
•
BIOS interrupts, instructions executed by programs, as an economical
way of calling routines in the BIOS (such as the video display or
communications services).
•
Hardware interrupts, issued by a device manipulating control lines, as
a way of requesting service from the BIOS (such as responding to a
timer tick or key depression).
•
Microprocessor interrupts, issued by the microprocessor itself under
certain circumstances (such as an attempt to divide by 0 or arithmetic
overflow).
All interrupts are vectored from low RAM, to allow an application to service
the interrupt with its own routine. The routine can be used to change the
normal response to an interrupt, or to provide a response where one is not
normally made (as indicated by IRET in the following table). The vectors are
restored to their defaults by a cold start (power up in non-resume mode, or
after emergency breakout or loss of all power).
The main vector addresses and default contents on MP2500 are
summarised in the following table. To change a vector, you can write direct
to memory or use the DOS 'set interrupt vector' function (see the MS-DOS
Programmer's Manual).
CAUTION: You must not change the vector for INT 2 (which
services NMIs), as NMIs are vital to operation of
MP2500. If you change this vector, MP2500 will stop
operating.
Chapter 19: The Interrupts 175