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Browse Prior Art Database

Bus Contention And Overload Detecting Transmitter

IP.com Disclosure Number: IPCOM000106890D
Original Publication Date: 1992-Jan-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 121K

Publishing Venue

IBM

Related People

Balliet, L: AUTHOR [+2]

Abstract

This article describes a technique and enabling hardware for fast detection of simultaneous transmissions for special-purpose signalling and detection of short circuit faults.

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

Bus Contention And Overload Detecting Transmitter

       This article describes a technique and enabling hardware
for fast detection of simultaneous transmissions for special-purpose
signalling and detection of short circuit faults.

      Communication architecture and protocols for serial data buses
provide for access to a shared network via various access control
techniques.  Invariably, when access is obtained, a unit starts
transmitting its message and continues until message completion.  A
maximum message length may be specified; however, messages frequently
can be very long.  There are techniques whereby a higher priority
source can interrupt a long low-priority message and thereby improve
high-priority message response time.  These are mainly applicable to
loop (ring) topology where units connect serially.  However, on a
parallel connected party line bus, the methods for inserting an
interrupt are not directly applicable.  The technique of this article
provides an instantaneous interrupt for party line buses.  It is
especially important to applications of bus architecture on
automobiles.  In addition to these applications, the technique can be
used to detect faults and abnormal loads important to error detection
and fault isolation.

      The concept is to permit high-priority message sources that
share a party line bus to interrupt a low-priority transmission by
superimposing signals of opposite polarity at predetermined bit times
in the message format.  A specially designed transmitter in the
low-priority unit detects the overload and signals its controller of
the interrupt.  This can be used with any of a number of different
bit formats.  Standard non-return to zero (NRZ) is used to
illustrate.  The message for mat, as is traditional, is defined to
contain "n" number of bits per word with each word having certain
predictable predefined bits.  For example, the first bit of a word
format will be a "START" bit and the last bit will be a parity bit.

      Fig. 1 shows a party line connection containing m parallel
units on a physically short bus such as that contained in a cabinet,
small room or on an automobile. Consider unit #1, a low-priority
unit, transmitting a long message.  Unit #3 sees the message on the
bus and requires issuing an interrupt.  Fig. 2 illustrates a typical
message with data transmitted by unit #1.  Unit #3 receives the
message, synchronizes its transmitter, and determines the parity bit
to be transmitted at word 2...