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Architecture for a Multi-Drop, Master-Sharing Communication Expansion System

IP.com Disclosure Number: IPCOM000100607D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 6 page(s) / 218K

Publishing Venue

IBM

Related People

Balliet, L: AUTHOR [+4]

Abstract

This article describes a multi-drop, master-sharing communication expansion system (hereafter referred to as communication bus) utilizing programmable RS232 or RS422/423 hardware shown in block diagram in Fig. 1.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 39% of the total text.

Architecture for a Multi-Drop, Master-Sharing Communication Expansion System

       This article describes a multi-drop, master-sharing
communication expansion system (hereafter referred to as
communication bus) utilizing programmable RS232 or RS422/423 hardware
shown in block diagram in Fig.  1.

      As future automotive diagnostic equipment evolves, it has
become evident that a requirement exists for attaching various test
equipment to a technician terminal.  The type of diagnostic devices
may include basic engine analyzers, anti-lock brake systems testers,
automated break-out boxes, exhaust gas analyzers, vehicle
communication links, second generation probe devices and others.

      The communication bus is designed to attach to any existing
RS232 or RS422/423 serial asynchronous I/O port that is capable of
being software controlled.  While the hardware I/O signals are the
same as those used in typical RS232 communication, the utilization of
those signals is modified to allow multi-drop capability as well as
meet other goals.

      A block diagram of the data section of the communication bus of
this disclosure is shown in Fig. 2. The design as proposed can
support "n" direct attachments referred to as channels (CHO through
CHn).  An additional special attachment is defined to conform to the
RS232 protocol.  This port is referred to as the "S-port".  All
channels support both receive (Rx) and transmit (Tx).  The hardware
supports half-duplex communication.

      Master or slave devices attach to the communication bus using
RS422 drivers (Tx 422) and receivers (Rx 422).  The communication bus
can be implemented so that standard programmable RS232 devices can
attach directly if the (Rx / Tx 422) and (Tx / Rx 422) devices are
residing on the communication bus backplane.  All data signals are
converted to RS422 compatibility to provide multi-drop capability.

      The protocol is such that a device must attach as either a
master type or a slave type.  The communication description along
with the communication handshake rules set forth later explain how
devices gain access as master devices.  The protocol is such that
only one device can "talk" at a time.

      An S-Port control signal is asserted as a logic low value to
disable the S-Port from transmitting or receiving signals.  The
S-Port control signal in this state also allows the transmit (Tx) bus
and the receive (Rx) bus to be logically tied together through a
bridge circuit.  This allows any attached master or slave device to
talk (when allowed to by protocol) and listen.

      When the S-Port control signal is asserted to a logic high
state by the current master, the S-Port driver and receiver are
enabled and standard communication can occur between the current
master and the standard RS232 device attached to the S-Port.

      A functional block diagram is shown in Fig. 3 for the control
logic section of the communication bus. ...