Browse Prior Art Database

Method of Sharing Interrupt Bus in Personal Computers

IP.com Disclosure Number: IPCOM000113273D
Original Publication Date: 1994-Aug-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 100K

Publishing Venue

IBM

Related People

Snidow, RE: AUTHOR

Abstract

Described is a hardware implementation for Personal Computers (PCs) that allows devices with different interrupt protocols to share an interrupt level in an AT-bus system. The functional capability of the PC is increased by enabling more interrupt driven devices to be attached to the AT-bus.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Method of Sharing Interrupt Bus in Personal Computers

      Described is a hardware implementation for Personal Computers
(PCs) that allows devices with different interrupt protocols to share
an interrupt level in an AT-bus system.  The functional capability of
the PC is increased by enabling more interrupt driven devices to be
attached to the AT-bus.

      Typically, devices which reside on the AT-bus generate
interrupts by causing a low-to-high transition on the appropriate
interrupt signal.  When two or more devices share an interrupt, each
must be capable of generating an interrupt independently and without
any interference from other devices on that interrupt signal line.  A
problem can arise in the event a device designed for operation on the
Micro Channel* (MC) must share an interrupt with an AT-device on the
AT-bus, or when an interrupt must be shared by a device which is not
properly designed for interrupt sharing.  The problem displays itself
as a device drives the interrupt signal low until such time as an
interrupt is needed; at that time the interrupt signal is driven high
to generate an interrupt.  The device cannot release the interrupt
signal, such as using a tri-state driver, because the low-to-high
transition would generate an interrupt and another device cannot
over-drive the low.  As a result, the interrupt cannot be shared.
Simply using an AND or OR function will not solve the problem as the
output of that function will also create the same problem (interrupts
must be shared by all devices on the AT-bus).

      The concept described herein provides AT-bus interrupt sharing
capability by permitting an IDE hardfile, that has been designed to
interface directly to an AT-bus with an exclusive interrupt, and a
Small Computer System Interface (SCSI) hardfile controller, developed
to interface to the MC or AT-bus with an exclusive interrupt, to
share the same interrupt signal.  The IDE hardfile device drives the
interrupt low until an interrupt is required.  The SCSI controller
requires external logic to interface to the AT-bus interrupt
structure.  The concept is applicable to other interrupts, such as
serial ports, parallel ports, video ports, etc.

      The Figure shows a circuit representation of the AT-bus
interrupt sharing method, and consists of the following:

o   Input conditioner 10 - used to correct the polarity of the input
    interrupt, such that the output of input conditioner 10 is a
    constant logical level until an interrupt is indicated by the
    input interrupt.  When an interrupt is indicated, input
    conditioner 10 will transition to the opposite logical leve...