U.S. patent application number 10/838650 was filed with the patent office on 2005-06-09 for network node with plug-in identification module.
This patent application is currently assigned to I/O Controls Corporation. Invention is credited to Ying, Jeffrey.
Application Number | 20050125565 10/838650 |
Document ID | / |
Family ID | 32176788 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050125565 |
Kind Code |
A1 |
Ying, Jeffrey |
June 9, 2005 |
Network node with plug-in identification module
Abstract
A network node includes a housing in which the electronics of
the network node are contained, the housing having an external port
to which a plug-in module can be physically attached. The plug-in
module contains a readable memory which, when the plug-in module is
attached, allows electronic interconnection between the electronics
of the network node and the readable memory. The readable memory
stores a unique node identifier which becomes associated with the
node, and can also store functional program code for the particular
node. Thus, a node can be easily and rapidly replaced or
reprogrammed, without the need for specialized equipment to
download the node identifier or functional program code, and
without the possibility of erroneous manual entry of the node
identifier. In operation, the node reads in its node identifier
from the appropriate address of the readable memory, and thereafter
sends and receives communications in accordance with the node
identifier it has read out from the plug-in module. In one
embodiment, the plug-in module takes the form of an enclosed
cylindrical unit having wrapped about its periphery at one end a
cylindrical attachment piece with inner threading, which connects
to a threaded extension on the node housing. Pins along the base of
the plug-in module fit snugly into opposing holes along the top of
the extension piece on the node housing, or vice versa. The network
node with plug-in module is particularly well suited for use in
large, distributed control network systems, such as a multi-bus
hierarchical control network.
Inventors: |
Ying, Jeffrey; (Glendora,
CA) |
Correspondence
Address: |
IRELL & MANELLA LLP
1800 AVENUE OF THE STARS
SUITE 900
LOS ANGELES
CA
90067
US
|
Assignee: |
I/O Controls Corporation
Azusa
CA
|
Family ID: |
32176788 |
Appl. No.: |
10/838650 |
Filed: |
May 3, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10838650 |
May 3, 2004 |
|
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09442369 |
Nov 17, 1999 |
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6732202 |
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Current U.S.
Class: |
709/253 |
Current CPC
Class: |
G05B 19/042 20130101;
G05B 2219/25107 20130101; G05B 2219/25296 20130101 |
Class at
Publication: |
709/253 |
International
Class: |
G06F 015/16 |
Claims
1. A network node for use in a control network, comprising: a node
housing, said node housing comprising an external port; a processor
contained within said node housing; a transceiver contained within
said node housing, said transceiver having a connection for an
external data bus; a detachable module adapted for connection to
said external port, said detachable module comprising an enclosed
module body; and a readable memory encapsulated within said
enclosed module body, said readable memory storing a unique node
identifier for the network node; wherein said readable memory is
accessible to said processor when said detachable module is
connected to said external port.
2-31. (canceled)
Description
RELATED APPLICATION INFORMATION
[0001] This application is a continuation of U.S. application Ser.
No. 09/442,369, filed on Nov. 17, 1999, hereby incorporated by
reference as if set forth fully herein.
BACKGROUND OF THE INVENTION
[0002] 1) Field of the Invention
[0003] The field of the invention pertains to methods and apparatus
for implementing a control network and, more particularly, to a
network node for use in a control network.
[0004] 2) Background
[0005] Automated control systems are commonly used in a number of
manufacturing, transportation, and other applications, and are
particularly useful to control machinery, sensors, electronics, and
other system components. For example, manufacturing or vehicular
systems may be outfitted with a variety of sensors and automated
electrical and/or mechanical parts that require enablement or
activation when needed to perform their predefined functions. Such
systems commonly require that functions or procedures be carried
out in a prescribed order or with a level of responsiveness that
precludes sole reliance on manual control. Also, such systems may
employ sensors or other components that require continuous or
periodic monitoring and therefore lend themselves to automated
control.
[0006] As the tasks performed by machinery have grown in number and
complexity, a need has arisen for ways to exercise control over the
various components of a system rapidly, efficiently and reliably.
The sheer number of system components to be monitored, enabled,
disabled, activated, deactivated, adjusted or otherwise controlled
can lead to difficulties in designing and implementing a suitable
control system. As the number of system components to be controlled
is increased, not only is the operation of the control system made
more complicated, but also the wiring and inter-connections of the
control system are likewise more elaborate. In addition, greater
reliance on automated control has resulted in larger potential
consequences if the automated control system fails.
[0007] Certain conventional types of distributed control network
use a hierarchical control structure with nodes to handle local
tasks. For example, one type of control network uses a dual-bus
architecture including a primary bus for a high-speed,
bi-directional communication link interconnecting a main (or
first-tier) data bus controller with distributed slave nodes. One
of the slave nodes acts as a second-tier data bus controller
connected to a secondary, low-speed data bus. A number of
second-tier slave nodes may be connected to the secondary data bus.
The first-tier and second-tier slave nodes may be connected to
various input/output ports for performing various local functions.
The main data bus controller, secondary data bus controller,
first-tier slave nodes, second-tier slave nodes, input/output ports
and other system components collectively form a hierarchical system
wherein the main data bus controller supervises the first-tier
slave nodes, including the second data bus controller, the second
data bus controller supervises the second-tier slave nodes, and the
first-tier slave nodes and second-tier slave nodes supervise their
assigned input/output functions.
[0008] A more elaborate control network system as conventionally
known is described, for example, in U.S. Pat. No. 5,907,486,
assigned to the assignee of the present invention. In the system
described therein, additional data buses may be added to the
hierarchical control network, so as to form additional second-tier
control loops each having a secondary data bus controller (master
node) and a set of second-tier slave nodes, and/or additional
lower-tier control loops, each having an Nth-tier data bus
controller (master node) and a set of Nth-tier slave nodes.
[0009] A problem that particularly affects large, distributed
control networks is re-configuring the system when network nodes
are replaced or added. A network node may be replaced because it
has failed electrically, or because additional functionality is
needed, or may be added to increase the capability or size of the
control network. Each network node requires a unique identifier, so
it can be referenced by the other nodes. Each network node is also
required to be programmed with its specific functionality. As
currently practiced, when network nodes are replaced, a computer or
special tool is needed to download the node identifier and/or
functional program code to the node. This task requires specialized
equipment, and is time-consuming and inconvenient. Moreover, a
mistake can be made in entering the node identifier manually, which
will cause the system to function improperly thereafter.
[0010] Likewise, when an existing network node needs to be
reprogrammed to change its functionality, the same sort of
specialized equipment is needed to download the new program or
change the program parameters. Again, this task is time-consuming
and inconvenient.
[0011] Accordingly, it would be advantageous to provide a mechanism
for allowing rapid and convenient association of a network node
with a node identifier, and rapid and convenient programming of a
newly added or existing network node.
SUMMARY OF THE INVENTION
[0012] According to one aspect of the invention, a network node for
use in a control network is provided, in which association of a
node identifier and/or functional program code with the node is
carried out in a rapid and convenient manner, without the need for
specialized equipment, and without the possibility of erroneous
manual entry of the node identifier.
[0013] In one embodiment, a network node includes a housing in
which the electronics of the network node are contained, including
one or more processors and various I/O functions. The housing
includes a port to which a plug-in module can be physically
attached. The plug-in module contains a readable memory which, when
the plug-in module is attached to the node housing, allows
electronic interconnection between the electronics of the network
node and the readable memory. The readable memory stores a unique
node identifier which becomes associated with the node, as well as,
if desired, the functional program code for the particular node. In
operation, the node reads in its node identifier from the
appropriate address of the readable memory, and thereafter sends
and receives communications in accordance with the node identifier
it has read out from the plug-in module.
[0014] In one embodiment, the plug-in module takes the form of an
enclosed cylindrical unit having wrapped about its periphery at one
end a cylindrical attachment piece with inner threading. The node
housing may have a short, cylindrically-shaped extension with outer
threading for receiving the cylindrical attachment piece. The
cylindrical attachment piece may be screwed onto the
cylindrically-shaped extension to secure the plug-in module to the
node housing. When the plug-in module is secure, pins along the
base of the plug-in module fit snugly into opposing holes along the
top of the extension piece on the node housing (or vice versa).
[0015] The network node configurations are described with reference
to a preferred multi-bus hierarchical control network, which
includes a first-tier common bus and a plurality of lower-tier
common buses. A first-tier master node controls a plurality of
first-tier slave nodes using the first-tier common bus for
communication. Each of the first-tier slave nodes may be connected
to a separate second-tier common bus, and each operates as a
respective second-tier master node for a plurality of second-tier
slave nodes connected to the particular second-tier common bus
associated with the first-tier slave/second-tier master node.
Likewise, each of the second-tier slave nodes may be connected to a
separate third-tier common bus, and each would then operate as a
respective third-tier master node for a plurality of third-tier
slave nodes connected to the particular third-tier common bus
associated with the second-tier slave/third-tier master node. A
preferred node comprises two separate transceivers, an uplink
transceiver for receiving control information, and a downlink
transceiver for sending out control information. Each node
therefore has the capability of performing either in a master mode
or a slave mode, or in both modes simultaneously.
[0016] Further variations and embodiments are also disclosed
herein, and are described hereinafter and/or depicted in the
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a diagram of a distributed control network with
two data buses as known in the prior art.
[0018] FIG. 2 is another diagram of a distributed control network
having a two data buses each configured in a loop configuration as
known in the prior art.
[0019] FIG. 3 is a circuit block diagram of a node that may be
employed in the distributed control network of FIG. 1 or FIG.
2.
[0020] FIG. 4 is a diagram showing a physical encasement of the
node shown in FIG. 3.
[0021] FIG. 5 is a block diagram of a preferred control network
architecture in accordance with one or more aspects of the present
invention.
[0022] FIG. 6 is a block diagram of a preferred node within the
control network architecture shown in FIG. 5.
[0023] FIG. 7 is a diagram of a hierarchical control network in
accordance with one embodiment of the present invention having
multiple second-tier buses.
[0024] FIG. 8 is a diagram of a hierarchical control network in
accordance with another embodiment of the present invention having
a third-tier bus.
[0025] FIG. 9 is a functional diagram of a multi-bus control
network illustrating one example of bus architectural layout and
node functionality according to one embodiment of the
invention.
[0026] FIG. 10 is a diagram of a node housing illustrating
attachment of a plug-in module.
[0027] FIG. 11 is a conceptual diagram illustrating electrical
connection of the readable memory within a plug-in module to the
electrical components of the node.
[0028] FIG. 12 is a conceptual diagram illustrating electrical
connection of the readable memory within a plug-in module to the
electrical components of the node, in accordance with an
alternative embodiment as described herein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0029] This application is generally related to U.S. Pat. No.
5,907,486 entitled "Wiring Method and Apparatus for Distributed
Control Network," U.S. patent application Ser. No. 08/854,160 filed
in the name of inventor Jeffrey Ying, entitled "Backup Control
Mechanism in a Distributed Control Network," U.S. patent
application Ser. No. 08/853,893 filed in the name of inventors
Jeffrey Ying and Michael Kuang, entitled "Fault Isolation and
Recovery In A Distributed Control Network," and U.S. patent
application Ser. No. 08/53,989 filed in the name of inventor
Jeffrey Ying, entitled "Multi-Tier Architecture for Control
Network," all of which foregoing are hereby incorporated by
reference as if set forth fully herein.
[0030] FIG. 1 is a block diagram showing the interconnection of
nodes in a particular type of control network 101 as known in the
art. The control network 101 comprises a main data bus controller
103 which is connected over a main data bus 104 to a plurality of
first-tier slave nodes 109 and 123. One first-tier slave node 123
connected to the main data bus 104 also functions as a second data
bus controller, and is connected to a second data bus 113. The
second data bus controller 123 is connected over the second data
bus 113 to a plurality of second-tier slave nodes 130. The main
data bus 104 forms a high-speed, bi-directional communication link
between the main data bus controller 103 and the first-tier slave
nodes 109 and 123, and the second data bus 113 forms a low-speed,
bi-directional communication link between the second data bus
controller 123 and the second-tier slave nodes 130.
[0031] The nature of the slave nodes 109, 123 and 130 depends in
part on the control application for which they are deployed. In a
transit vehicle or railcar, for example, the master data bus
controller 103 and the slave nodes 109, 123 and 130 may each be
assigned to control a particular section of the vehicle or railcar,
or may be assigned to control particular input and output
functions. For each slave node 109, 123 and 130 in FIG. 1, various
control signals are shown connected to the nodes such as to
illustrate one exemplary arrangement of control functionality.
[0032] In operation, the main controller 103 communicates with the
first-tier slave nodes 109 and 123 using the main data bus 104 as a
high speed bi-direction link. An exemplary baud rate for
communications over the main data bus 104 is 256 k. The main data
bus controller 103 is generally responsible for delegating control
commands to the first-tier slave nodes 109 and 123, and for
responding to status information and events communicated to the
main data bus controller 103 over the main data bus 104. Each of
the first-tier slave nodes 109 and 123 receives commands from the
main data bus controller 103, and issues appropriate commands over
their respective control lines. In a similar manner, the second
data bus controller 123 communicates with the second-tier slave
nodes 130 using the second data bus 113 as a low speed bi-direction
link (having a baud rate of, e.g., 9.6 k), and instructs the
second-tier slave nodes 130 to carry out certain control functions,
or responds to status messages or events relayed to the second data
bus controller 123 from the second-tier slave nodes 130.
[0033] FIG. 2 is a diagram showing the layout or architecture of
the FIG. 1 control network. The control network 201 shown in FIG. 2
comprises a main data bus controller 203 which is connected to a
main data bus 204. The main data bus 204 is physically connected to
a plurality of first-tier slave nodes 209 and 223. As explained
with respect to the control network 101 shown in the FIG. 1, one of
the first-tier slave nodes 223 also functions as a second data bus
controller 223, and is connected over a second data bus 213 to a
plurality of second-tier slave nodes 230. The main data bus 204 is
configured in a loop such that it passes through each of the
first-tier slave nodes 209 and 230 and returns to rejoin the main
data bus controller 203. In this way, should the wires of the main
bus 204 become severed, the main data bus controller 203 will still
be connected to the first-tier slave nodes 209 and 223 and will not
necessarily lose control over the system. Similarly, the second
data bus 213 is configured in a loop such that it passes through
each of the second-tier slave nodes 230 and returns to rejoin the
second data bus controller 223, thereby providing an architecture
resilient to potential severing of the wires of the second data bus
113. Each of the main data bus controller 203, first-tier slave
nodes 209 and 223, and second-tier slave nodes 230 may be connected
to a plurality of control signals for performing control or sensor
functions, or various other input and output functions as necessary
for the particular control application.
[0034] The control network 201 shown in FIG. 2 thus utilizes a
dual-bus architecture to perform control functions. Because of the
hierarchical architecture of the control system 201, relatively low
baud rates on the second data bus 213 can be tolerated, leading to
reduced system size, cost and complexity over traditional
non-hierarchical, relay-based systems. The slower speed on the
secondary data bus 213 also reduces the system's susceptibility to
electromagnetic interference, a potential problem in certain
control system environments (such as railcars).
[0035] Each node, whether master data bus controller 203,
first-tier slave node 209 or 223, or second-tier slave node 230,
includes means for performing computations necessary for its
functionality, and is configured with components such as a central
processing unit (CPU) and memory. FIG. 3 is a more detailed block
diagram of a node 301 (such as the master data bus controller 203,
a first-tier slave node 209 or 223, or a second-tier slave node
230) that may be employed in the control network of FIG. 2. The
node 301 comprises a CPU 315 connected to a power control block 317
and a transceiver 305. The node 301 is also connected to power
signal lines 316, which connect to the power control block 317. The
node 301 may communicate over communication signal lines 304, which
are connected to the transceiver 305. An electrical erasable
programmable read-only memory (EEPROM) 306 stores programming
information utilized by the CPU 315 for carrying out certain
programmable functions. The CPU 315 has access to a random access
memory (RAM) (not shown) and read-only memory (ROM) (not shown) as
needed for the particular application.
[0036] The CPU 315 is connected to a keyboard and display interface
block 320. The keyboard and display interface block 320 is
connected to status LEDs 307, relays 321, and LED display 311 and a
keypad 331. The node 301 is thereby can accept manual inputs (e.g.,
from the keypad 331) or receive sensor inputs (e.g., over relays
321), and can display operational status using status LEDs 301 or
LCD display 311.
[0037] The node 301 further comprises a network controller 322
which preferably comprises a second CPU. The network controller 322
is connected to a second transceiver 323 which is connected to a
second pair of communication signal lines 314. The network
controller also outputs power signal lines 336.
[0038] In operation, node 301 may communicate over two different
data buses using transceivers 305 and 323. Thus, node 301 may
communicate over a first data bus (such as data bus 204 shown in
FIG. 1) by receiving and transmitting signals over communication
signal lines 314 using transceiver 323, under control of the
network controller 322. The node 301 may communicate over a second
data bus (such as data bus 213 shown in FIG. 2) by transmitting and
receiving signals over communication signal lines 304 using
transceiver 305, under control of CPU 315. The CPU 315 and network
controller 322 may transfer information back and forth using a
shared memory (not shown). The node 301 may serve as both a "slave"
unit with respect to the first data bus 204 and a "master" unit
with respect to the second data bus 213. By interconnecting a
plurality of nodes 301 in an appropriate configuration, a
hierarchical control network with two data buses (as shown in FIG.
2) may be established.
[0039] Each node 301 such as shown in FIG. 3 is housed in a rugged,
potted case made of a suitable lightweight material such as
aluminum that provides environmental protection and allows for heat
dissipation. FIG. 4 is a diagram showing an exemplary physical
casing 401 of a module or node 301 such as shown in FIG. 3. The
casing 401 can be quite small; in the example of FIG. 4, the casing
401 measures approximately 2.1' by 3.75', and is 0.825' in
thickness.
[0040] A problem that can occur in operation of a control network
such as shown in FIG. 2 is that if the master data bus controller
203 fails then operation of the entire system could be jeopardized.
A possible solution would be to provide a redundant master data bus
controller that has the same functionality as the primary master
data bus controller 203 in all respects. Upon detecting a failure
of the primary master data bus controller 203, the backup master
data bus controller could shut down the primary master data bus
controller 203 and take over control of the network.
[0041] While having such a separate, redundant master data bus
controller for backup purposes may provide a solution where the
primary master data bus controller 203 fails, it falls short of
being a complete solution. As an entirely separate controller
having complete functional and hardware redundancy of the primary
master data bus controller 203, incorporation of the backup master
data bus controller effectively doubles the cost of implementing
the master data bus controller 203. Also, another drawback is that
if both the master data bus controller 203 the backup master data
bus controller fail, then operation of the entire system would be
jeopardized and operation could come to complete halt.
[0042] In addition to the possibility of the master data bus
controller 203 failing, the second data bus controller 223 could
also be subject to failure. While a redundant second data bus
controller for backup purposes could be provided, the cost of
implementing the second data bus controller would be essentially
doubled, and the system is still subject to potentially complete
failure should the second data bus controller also fail. Moreover,
adding redundant data bus controllers could complicate the wiring
of the system.
[0043] A preferred embodiment of the invention overcomes one or
more of the above problems by providing redundant backup control
for the master data bus controller 203 or other type of master
node, the second data bus controller 223 or similar types of nodes,
and, if further nested control levels exist (as described, for
example, in later embodiments herein), other sub-controllers for
those control levels.
[0044] FIG. 5 is a block diagram of a preferred embodiment of a
control network 501 having redundant backup control capability for
a master node at each bus level of the control network 501.
Hereinafter, the node acting as the master bus controller for a
particular bus will be referred to as the "master node" for that
particular bus, and all the other nodes on that bus will be
referred to as "slave nodes" for that particular bus. In the
control network shown in FIG. 5, a master node 503 and a plurality
of first-tier slave nodes 523 are connected to a main data bus 504.
In a preferred embodiment of the invention, each of the slave nodes
523 is configured or can be configured to control a secondary data
bus. For example, the first-tier slave node 523c is shown connected
to a secondary data bus 523 in the control network 501. The
first-tier slave node 523c functions as a second-tier master node
with respect to second-tier slave nodes 533 connected to the
secondary data bus 513. Others of the first-tier slave nodes 523
can also serve as second-tier master nodes and be connected to
different secondary buses having additional second-tier slave
nodes. A multi-level or multi-tiered hierarchical control network
is thereby established.
[0045] Each of the master node 503, first-tier slave nodes 523,
second-tier slave nodes 533, and other lower-level slave nodes (not
shown in FIG. 5) are referred to hereinafter generically as "nodes"
and are designated as nodes 530 in FIG. 5. In one aspect of a
preferred embodiment as shown in FIG. 5, each of the nodes 530 has
substantially the same hardware configuration and can therefore
function as either a master node or a slave node, depending upon
how the control network 501 is configured. Each data bus, along
with the nodes attached to it, are generally referred to as a cell,
and the master node connected to the data bus is referred to as a
"cell controller" for that particular cell. As explained in more
detail hereinafter, each node 530 configured as a master node
transmits and receives messages over the data bus for the cell it
controls. Each node 530 configured as a slave node remains in a
listen mode, receiving but not transmitting messages over that data
bus, unless specifically requested to transmit information over the
data bus by the master node. Any number of the slave nodes can,
even though operating as a slave node with respect to an upper
tier, be simultaneously operating as a master node with respect to
other lower-tier slave nodes at a different cell sub-level.
[0046] A preferred embodiment of the invention, as noted, comprises
a mechanism for redundant backup control of any node functioning as
a master node at any level or sub-level of the control network 501.
As generally described, in operation of a preferred embodiment of
the invention the slave nodes connected to a particular data bus
monitor the data bus while in a listen mode and await periodic
signals from the master node for that data bus. Upon a failure to
receive a signal from a master node within an expected time, the
slave nodes connected to that data bus begin a wait period (which
is preferably a different wait period for each slave node connected
to the data bus). When the wait period elapses, the slave node
determines that a failure in the master node for the particular
data bus has occurred, and takes steps to take over the
functionality of the master node. Each of the slave nodes is
programmed with a different wait period, so that there is no
contention for replacing the master node when a master node failure
has occurred. In one aspect, backup control of each master node is
prioritized, such that there is a specific order in which the slave
nodes can potentially take over control of the master node
functionality when a failure has occurred.
[0047] In more detail, again with reference to FIG. 5, one of the
nodes 530 attached to the main data bus 504 is configured as a
master node 503. The other nodes 530 attached to the main data bus
504 (in this example numbering four such nodes 530) are configured
as first-tier slave nodes 523, meaning that they receive but do not
transmit master-control signals over the main data bus 504. The
first-tier slave nodes 523 may, however, from time to time send
responsive signals or status signals over the main data bus
504.
[0048] In a preferred embodiment, each of the first-tier slave
nodes 523 may be configured as a second-tier master node
controlling a secondary bus. One such example is shown in FIG. 5,
wherein first-tier slave node 523c is connected to a secondary data
bus 513. A plurality of other nodes 530 are also attached to the
secondary bus data 513, and serve as second-tier slave nodes 533.
There are three such second-tier slave nodes 533 in the example
shown in FIG. 5. With respect to the secondary data bus 513, the
first-tier slave/second-tier master node 523c transmits
master-control signals to the second-tier slave nodes 533. The
second-tier slave nodes 533 ordinarily operate only in a listen
mode, but from time to time may send responsive messages or status
messages to the second-tier master node 523c. The other first-tier
slave nodes 523a, 523b and 523d may similarly be connected as
second-tier master nodes (i.e., cell controllers) each controlling
its own secondary bus or cell.
[0049] While the control network 501 shown in FIG. 5 has four
first-tier slave nodes 523 and three second-tier slave nodes 533,
the number of first-tier slave nodes 523 and second-tier slave
nodes 533 is limited only by the ability of the master node to
communicate with the slave nodes over the particular data bus.
There may be more slave nodes or fewer slave nodes on each bus than
shown in the control network 501. In a preferred embodiment, there
are no more than eight such cell controllers, although more than
eight may be used so long as processing capacity and speed
permit.
[0050] In addition, further levels of control nesting beyond two
data buses may also be provided, using a similar approach to the
two data bus method. Thus, for example, one or more of the
second-tier slave nodes 533 may be configured as a third-tier
master node controlling its own tertiary or third-tier data bus.
While FIG. 5 only shows two nested control levels, the same control
concepts would apply to a control network architecture having
additional nested control levels. Examples of control networks
having more than two data buses are depicted in FIGS. 7, 8 and 9
and described in more detail hereinafter.
[0051] In a preferred embodiment, communication over the main data
bus 504 and the secondary data bus 513 (or buses, if appropriate)
is time-multiplexed such that only one node 530 is transmitting
over a particular data bus at a given time. Usually, each
transmitted message will be targeted for a specific destination
node 530, which may be specified by address bits in the transmitted
message. However, in some embodiments broadcast messages may also
be used targeted to multiple nodes 530.
[0052] Responsibilities for tasks, or groups of tasks, may be
assigned to specific nodes 530. For example, each of the first-tier
slave nodes 223 may be assigned a distinct sphere of
responsibility. Similarly, each of the second-tier slave nodes 533
may be assigned a distinct sphere of responsibility. Examples of
tasks that may be assigned to different nodes 530 are described for
an exemplary control network later herein, with respect to FIG.
9.
[0053] Each of the nodes 530 preferably comprises an uplink
transceiver 507, a downlink transceiver 508, and a switch 509. Each
of the nodes 530 receives signals over its downlink transceiver
508. Over the main data bus 504, the first-tier master node 503
transmits master-control signals to each of the first-tier slave
nodes 523. From time to time, according to the programmed control
protocol, the first-tier slave nodes 523 respond to the
master-control signals, or otherwise send status messages to the
first-tier master node 503 when events occur specific to that
first-tier slave node 523. Otherwise, the first-tier slave nodes
523 do not ordinarily communicate with each other.
[0054] In a similar manner, over each secondary data bus (such as
secondary data bus 513), the second-tier master node 523 (for
example; first-tier slave/second-tier master node 523c in FIG. 5)
transmits master-control signals to each of the second-tier slave
nodes 533 connected to the same secondary data bus. From time to
time, according to the programmed control protocol, the second-tier
slave nodes 533 respond to the master-control signals, or otherwise
send status messages to the second-tier master node 523c when
events occur specific to that second-tier slave node 533.
Otherwise, the second-tier slave nodes 523 do not ordinarily
communicate with each other.
[0055] Communication between nodes is preferably carried out using
half-duplex time division multiplexing. In typical operation, the
master node polls each of the slave nodes periodically. Each of the
nodes is preferably provided with a unique node identification
number or address that distinguishes it from all other nodes of the
control network. The master node sends a control message to each
slave unit in turn, using the node identification number or address
to identify the intended destination. Each of the slave nodes
receives the control message but only reacts if it recognizes its
own node identification number or address in the control message.
The slave node takes the actions requested by the control message
received from the master node. Within a designated time period
after receiving the control message, the slave node responds to the
master node with an acknowledgment message. Each of the slave nodes
are polled in turn so that the master node can keep track of events
happening throughout the system.
[0056] A communication protocol is preferably established so as to
avoid collisions on each of the data buses. A simple and effective
communication protocol is one in which the master node for the
particular data bus sends a control message to a particular slave
node, which responds with an acknowledgment or status message
within a predetermined amount of time before the master node
contacts another slave node. Slave nodes generally do not initiate
communication without being first polled by the master node. The
master node may also send out a broadcast control message that is
intended for receipt by more than one of the slave nodes. The
broadcast control message can comprise a node identification number
or address that instructs a single particular node to respond to
the broadcast control message. Usually, the single node selected
for response will be the most critical node requiring receipt of
the broadcast control message.
[0057] Failure of the current master node (at any of the control
levels) commonly results in the master node either failing to
transmit, or else transmitting improper control information to the
slave nodes over the data bus. According to a preferred redundant
backup control protocol, the slave nodes periodically receive
master-control messages from the master node and, in the event that
proper master-control messages fail to appear, initiate a failure
mode response procedure.
[0058] Detection of and response to a failure mode condition may be
explained in greater detail with reference to FIG. 6, which is a
block diagram of a preferred embodiment depicting most of the main
components of a node (such as any of nodes 530 shown in FIG. 5).
Because failure mode detection and response is carried out by a
node 530 operating as a slave node, the following discussion will
assume that the node 603 shown in FIG. 6 is initially configured as
a slave node. Further, for simplicity of explanation, it will be
assumed that the node 603 shown in FIG. 6 is a first-tier
slave/second-tier master node connected to a main bus and a
secondary bus (such as first-tier slave/second-tier master node
523c connected to the main data bus 504 and secondary data bus 513
in FIG. 5), although the same node circuit configuration is
preferably used for each of the nodes 530, regardless of control
level, for ease of construction and flexibility purposes.
[0059] In the node block diagram of FIG. 6, a node 603 is shown
connected to a first bus (e.g., main bus) 604. The node 603
comprises an uplink transceiver 611, a downlink transceiver 621, a
CPU 612 connected to the uplink transceiver 611, and another CPU
622 connected to the downlink transceiver 621. Both CPUs 612, 622
are preferably connected to a dual-port RAM 618, and each CPU 612,
622 is connected to a ROM program store 614 and 624, respectively.
The second CPU 622 is connected through an appropriate interface to
I/O ports 654, which may comprise sensor inputs, control signal
outputs, status LEDs, LCD display, keypad, or other types of
external connections. It will be understood that the node 603 of
FIG. 6 can have all the components and functionality of the node
301 shown in FIG. 3; however, in FIG. 6 only certain basic
components needed for explaining the operation of the invention are
depicted.
[0060] Each node 603 is preferably capable of both sending and
receiving messages (e.g., control instructions). Typically, the
uplink transceiver 611 operates in a "slave" mode whereby the node
603 receives control instructions using the uplink transceiver 611
and then responds thereto, and the downlink transceiver 621
operates in a "master" mode whereby the node 603 issues control
instructions (e.g., polls slave nodes) and awaits a response from
other nodes after sending such control instructions.
[0061] The downlink transceiver 621 of the node 603 is connected to
a secondary data bus 652, to which is also connected a plurality of
second-tier slave nodes 651 (assuming the node 603 is a first-tier
slave/second-tier master node). The node 603 thereby functions as a
first-tier slave node with respect to the main data bus 604,
receiving with its uplink transceiver 611 first-tier master-control
signals over the main bus 604 from a first-tier master node (such
as master node 503 shown in FIG. 5), and also functions as a
second-tier master node with respect to the secondary data bus 652,
transmitting second-tier master-control signals with its downlink
transceiver 634 to second-tier slave nodes 651.
[0062] The node 603 also comprises a pair of switches 635a, 635b
connected between the downlink transceiver 621 and the signal lines
643a, 643b of the main data bus 604. In normal operation, the
switches 635a, 635b remain open (unless the node 503 is also the
first-tier master node, such as master node 503 shown in FIG. 5, in
which case the switches 635a, 635b would be closed), and the
downlink transceiver 621 is thereby isolated from the main data bus
604. However, when a first-tier master node failure condition is
detected, switches 635a, 635b are closed, enabling the downlink
transceiver 621 to take over for the first-tier master node. The
downlink transceiver 621 would therefore function simultaneously as
master node with respect to both the main data bus 604 and the
secondary data bus 652.
[0063] In a preferred embodiment, detection of a master node
failure condition on the main data bus 604 is accomplished using a
timer mechanism, such as a hardware timer 613 accessible (either
directly or indirectly) by the CPU 612 that is connected to the
uplink transceiver 611. According to a preferred control protocol
(assuming the node 603 is a first-tier slave/second-tier master
node), the uplink transceiver 611 of node 603 receives first-tier
master-control signals periodically from the first-tier master node
(such as master node 503 in FIG. 5). The master-control signals
may, for example, request status information from the node 603, or
instruct the node 603 to carry out certain control or input/output
functions. The node 603 ordinarily responds by carrying out the
requested functions and/or sending an acknowledgment or status
signal to the first-tier master control node using the uplink
transceiver 611.
[0064] Timer 613 times out a wait period between master-control
signals received from the first-tier master control node. In a
preferred embodiment, each time the uplink transceiver 611 receives
a master-control signal from the first-tier master node that is
recognized as an appropriate master-control signal within the
particular programmed control protocol (whether or not the
master-control signal is directed to the particular node 603), the
CPU 612 connected to the uplink transceiver 612 resets the timer
613. If the timer 613 ever times out, then CPU 612 responds by
asserting a failure mode response procedure. The timing out of
timer 613 may result in an interrupt to CPU 612 in order to inform
the CPU 612 of the failure to receive master-control signals, or
else the CPU 612 may periodically monitor the timer 613 and, when
the CPU 612 notices that the timer 613 has timed out, assert a
failure mode response procedure.
[0065] When a failure mode condition is detected, the CPU 612 sets
a failure mode status bit in a predetermined flag location within
the dual-port RAM 618. The other CPU 622 periodically monitors the
failure mode status bit in the dual-port RAM 618 and is thereby
informed when a failure occurs. Alternatively, instead of the CPUs
612, 622 communicating through the dual-port RAM 618, timer 613 can
directly inform CPU 622 when a failure to receive master-control
signals has occurred (i.e., when timer 613 has timed out).
[0066] When the CPU 622 has been informed or otherwise determined
that a failure mode condition exists, and that the first-tier
master node has presumably failed, the CPU 622 sends a signal over
control line 633 to close switches 635a, 635b, thereby connecting
the downlink transceiver 621 to the main bus 604. From that point
on, the CPU 622 performs as the first-tier master node with respect
to the main bus 604. The node 603 can continue to receive
information over the main data bus 604 using the uplink transceiver
611. Alternatively, the node 603 may thereafter perform all
transmission and reception over both the main bus 604 and the
secondary bus 652 using the downlink transceiver 621. When the
failure mode is entered, the CPU 622 may be programmed so as to
directly carry out the I/O port functions for which it previously
received instructions from the first-tier master node, or the node
603 may send master-control signals to its own uplink transceiver
611 and thereby continue to carry out the I/O port functions as it
had previously been doing. In other words, the node 603 can give
itself control instructions over the main data bus 604 so that it
can continue to perform its previously assigned functions. If,
after taking over for the first-tier master node, the node's
downlink transceiver 611 should fail, the node 603 can still
continue to perform its control functions when the next slave node
takes over control as the new first-tier master node (as later
described herein), because its uplink transceiver 611 continues to
function in a normal manner.
[0067] According to the above described technique, the node 603
thereby substitutes itself for the first-tier master node upon the
detection of a first-tier master node failure as indicated by the
failure to receive the expected first-tier master-control signals.
Should the node 603 fail, either before or after taking over
control for the first-tier master node, the next first-tier slave
node would take over and become the first-tier master node in a
similar manner to that described above.
[0068] Referring again to FIG. 5, the order in which the first-tier
slave nodes 523 take over for the first-tier master node 503 is
dictated by the wait period timed out by the timer 613 of the
particular first-tier slave node 523. The timer 613 (see FIG. 6)
for each first-tier slave node 523 is programmed or reset using a
different time-out value. A first-tier slave node 523 only asserts
a failure mode condition when its internal timer 613 reaches the
particular timeout value programmed for that particular node
523.
[0069] While the programmed wait periods for the internal timer 613
in each first-tier slave node 523 can vary depending upon the
control application, illustrative wait periods are programmed in
ten millisecond increments. Thus, for example, first-tier slave
node 523a could be programmed with a 10 millisecond wait period;
the next first-tier slave node 523b could be programmed with a 20
millisecond wait period; the next first-tier slave node 523c could
be programmed with a 30 millisecond wait period; and the last
first-tier slave node 523d could be programmed with a 40
millisecond wait period; and so on. First-tier slave node 523a
would take over as the first-tier master node if 10 milliseconds
elapses without it receiving any proper first-tier master-control
signals; the next first-tier slave node 523b would take over as the
first-tier master node if 20 milliseconds elapses without it
receiving any proper first-tier master-control signals; the next
first-tier slave node 523c would take over as the first-tier master
node if 30 milliseconds elapses without it receiving any proper
first-tier master-control signals; and so on.
[0070] Use of 10 millisecond increments for the wait periods in the
above example is considered merely illustrative, and the actual
wait periods should be selected depending upon the time criticality
of the control messages, and the number of messages that may be
missed before a high enough degree of certainty is established that
the master node has failed. For example, if a slave node expects to
observe a control-message signal on the data bus no later than
every 5 milliseconds, then the slave node may be programmed to
assert a failure mode condition after a wait period corresponding
to the absence of a predefined number of messages--for example,
twenty messages (i.e., 100 milliseconds). If critical aspects of
the system requiring master node control need to be serviced in a
shorter time period, then the wait period would have to be reduced
to accommodate the time-sensitive components of the system.
[0071] The order in which the slave nodes take over for the master
node need not be dictated by the relative position in the control
loop of the slave node with respect to the master node, but rather
may be dictated according to the programmed wait period in each
slave node. Flexibility is thereby provided in the order of
priority in which the slave nodes take over for the master node in
the event of a failure event.
[0072] Accordingly, by use of the inventive techniques described
herein, redundant backup for the first-tier master node 503 is
provided. Such redundant backup control is provided without
requiring additional physical nodes to be located within the
control system, and without having to provide wiring for such
additional physical nodes to the buses 504 or 513. The redundant
backup for the master node 504 is also accomplished while resolving
contention problems that might otherwise occur if each of the
first-tier slave nodes 523 were programmed with the identical
timeout period.
[0073] In a preferred embodiment, redundant backup control is
provided in a similar manner for the secondary data bus 513, and
each additional data bus that may be provided in the system (e.g.,
in systems such as shown in FIGS. 7, 8 or 9). Thus, each of the
second-tier slave nodes 533 is preferably configured with the
circuitry shown for node 603 in FIG. 6, and each of the second-tier
slave nodes 533 can therefore substitute itself for the first-tier
slave/second-tier master node 523c if the first-tier
slave/second-tier master node 523c fails.
[0074] If a particular node is operating as a master node for two
buses as a result of a failure of the master node on a higher-tier
bus, and the node operating as such fails, then it is possible that
two different nodes will take over for the failed node, one node
taking over on each bus. For example, supposing that first-tier
slave/second-tier master node 523c has already taken over as the
first-tier master node due to a failure of the master node 503, and
further suppose that first-tier slave/second-tier master node 523c
too fails, then the next first-tier slave node 523d would take over
as the first-tier master node with respect to the main data bus
504, but the first second-tier slave node 533a would take over as
second-tier master node with respect to the secondary data bus
513.
[0075] In the above manner, despite the failure of one or more
nodes, substantial functionality of the control system as a whole
can be maintained. A failed node is essentially discarded or
bypassed to the extent possible so as to maintain the highest
possible degree of continued operability. Furthermore, because
certain parts of the system will continue operate despite the
failure of the master node, identification of the failed node by
engineers or maintenance personnel should be simplified by being
able to identify the inoperative portion of the system that has
become isolated due to the failure.
[0076] In one aspect, separation of responsibility in each node 603
of master functions and slave functions between two different CPU's
each operating with a different transceiver allows the node 603 to
potentially continue operating as either a master node or a slave
node should one of the CPU's fail, providing that the failure does
not disrupt both of the transceivers at the node 603.
[0077] In a preferred embodiment, the nodes 530 of FIG. 5 are wired
using a single cable connecting all of the nodes 530 in a loop
configuration. Details of such a wiring technique are described in
U.S. Pat. No. 5,907,486 entitled "Wiring Method and Apparatus for
Distributed Control Network," assigned to the assignee of the
present invention, and previously incorporated herein by
reference.
[0078] In a preferred embodiment, the nodes 530 of FIG. 5 are
configured with fault isolation and recovery circuitry in the case
of a short circuit or similar event. Details of such fault
isolation and recovery circuitry are described in copending U.S.
application Ser. No. 08/853,893 entitled "Fault Isolation and
Recovery In A Distributed Control Network," previously incorporated
herein by reference.
[0079] FIGS. 7, 8 and 9 depicts various embodiments having more
than two data buses, so as to provide additional levels of control
beyond that afforded by a dual-bus architecture. Each of the nodes
shown in FIGS. 7, 8 and 9 is preferably configured to include the
circuitry shown for preferred node 603 in FIG. 6. FIG. 7 shows an
example of a system architecture for a control network having three
data buses 704, 714 and 724. A first-tier master node 703 and a
plurality of first-tier slave nodes 712 are connected to the main
data bus 704. One of the first-tier slave nodes 712, designated as
A1 in FIG. 7, operates as a second-tier master node, and is
connected to the second data bus 714 along with a plurality of
second-tier slave nodes 722. Another of the first-tier slave nodes
712, designated as D1 in FIG. 7, operates as another second-tier
master node, and is connected to the third data bus 724 along with
another plurality of second-tier slave nodes 732. The other
first-tier slave nodes 712, designated B1 and C1 in FIG. 7, could
also be configured as master nodes of a second-tier bus. FIG. 7
thereby provides a hierarchical control network 701 having two
control levels or tiers, and three data buses.
[0080] FIG. 8 shows an example of a system architecture for a
control network having four buses 804, 814, 824 and 834. In a
similar manner to FIG. 7, a first-tier master node 803 and a
plurality of first-tier slave nodes 812 are connected to the main
data bus 804. One of the first-tier slave nodes 812, designated as
A1 in FIG. 8, operates as a second-tier master node, and is
connected to the second data bus 814 along with a plurality of
second-tier slave nodes 822. Another of the first-tier slave nodes
812, designated as D1 in FIG. 8, operates as another second-tier
master node, and is connected to the third data bus 824 along with
another plurality of second-tier slave nodes 832. One of the
second-tier slave nodes 832 connected to the third data bus 824,
denoted as A2' in FIG. 8, operates as a third-tier master node with
respect to the fourth data bus 834, which is connected to a
plurality of third-tier slave nodes 842. FIG. 8 thereby provides a
hierarchical control network 801 having three control levels or
tiers, and four data buses.
[0081] It will be appreciated that, expanding the approach used in
FIGS. 7 and 8, additional control levels may be created by adding
successive lower control tiers, or additional slave nodes at any
particular tier may be configured as cell controllers to control
additional localized data buses. A great deal of flexibility is
thereby provided in establishing a hierarchical control structure
suitable for many different control applications.
[0082] FIG. 9 is a diagram showing, from a functional standpoint,
an example of a particular control application having multiple data
buses in accordance with the hierarchical control principles
discussed herein. In FIG. 9, a control network 901 comprises a
master node 904 which is connected to a plurality of slave nodes
923, 924, 925 and 926, each of which is assigned a particular
sphere of responsibility within the control network. A main bus 903
forms a communication link between the master node 904 and the
slave nodes 923, 924, 925 and 926.
[0083] Generally, the nature of the slave nodes 923, 924, 925 and
926 depends in part on the control application in which they are
deployed. In the example of FIG. 9, the slave nodes 923, 924, 925
and 926 are deployed in a vehicle or railcar, and so the slave
nodes 923, 924, 925 and 926 have functionality suited for such a
control application. For example, the slave nodes include a slave
node 923 operating as a rear section controller, a slave node 924
operating as a central section controller, a slave node 925
operating as a front section controller, and a slave node 926
operating as a panel controller. There may also be additional slave
nodes if required.
[0084] Each of slave nodes 923, 924, 925 and 926 are considered
first-tier slave nodes in the illustrative embodiment shown in FIG.
9. In the control network 901 of FIG. 9, two of the first-tier
slave nodes 923, 924 also act as second-tier master nodes for
additional data buses. Thus, first-tier slave node 923 operates as
a second-tier master node with respect to a second data bus 913,
and first-tier slave node 924 operates as a second-tier master node
with respect to a third data bus 914. First-tier slave/second-tier
master node 923 is connected to a plurality of second-tier slave
nodes 931, 932, 933 and 934, which may each be assigned a
sub-sphere of responsibility in the cell controlled by the rear
section controller. The second-tier slave nodes may therefore
include, for example, a slave node 931 operating as a transmission
controller, a slave node 932 operating as an engine sensor and
controller, a slave node 933 operating as an air conditioner
controller, and a slave node 934 operating as a light indicator
controller.
[0085] Similarly, first-tier slave/second-tier master node 924 is
connected to another plurality of second-tier slave nodes 941, 942
and 943, each of which may be assigned a sub-sphere of
responsibility in the cell controlled by the central section
controller. The second-tier slave nodes may therefore include, for
example, a slave node 941 operating as a rear door controller, a
slave node 942 operating as a light controller, and a slave node
943 operating as a magnetic breaker controller.
[0086] Each of the first-tier slave nodes 923, 924, 925 and 926
(even if operating as a second-tier master node) may be connected
to one or more input/output modules 930. For example, the slave
node 925 operating as a front section controller may be connected
to a front door control module 951, a kneeling mechanism control
module 952, a wheel chair platform control module 953, and a
headlight output module 954. Likewise, the slave node 926 operating
as a panel controller may be connected to an indicator module 961,
an instrument module 962, a control switch module 963, and other
miscellaneous modules 964. Virtually any type of input/output or
control function may represented as a module 930. In each instance,
the respective slave node 923, 924, 925 and 926 controls the
input/output modules 930 connected to it.
[0087] The master node 904 may be connected to a computer 907
through an interface 906 (such as an RS-232 interface), if desired.
Through the computer 907, the master node 904 can be instructed to
execute certain functions or enter certain control modes. Also, the
master node 904 can be monitored or reprogrammed through the
computer 907.
[0088] In operation, the master node 904 communicates with the cell
controllers 923, 924, 925 and 926 using the main bus 903. The
master node 904, as previously described, is generally responsible
for delegating control commands to the slave nodes 923, 924, 925
and 926, and for responding to status information and events
communicated to the master node 904 over the main bus 903. Each of
the slave nodes 923, 924, 925 and 926 receives commands from the
master node 904, and issues appropriate commands to their
respective second-tier slave nodes 931-934 or 941-943, or
input/output modules 930.
[0089] Generally, the slave nodes are disposed in physical
locations near the mechanisms which they control. The main data bus
904 and secondary data buses 913, 914 each form a loop connecting
the various nodes connected to the bus in a continuous fashion. The
data buses 904, 913 and 914 are not restricted to any particular
baud rate. Rather, communication may be carried out over each data
bus 904, 913 and 914 at a rate that is suitable for the particular
control application. Moreover, there is no particular requirement
that the data buses in the FIG. 9 control network (or the more
generalized control networks shown in FIGS. 7 and 8) be serial data
buses. Rather, the data buses may be parallel data buses in
situations, for example, where a high data bandwidth is
required.
[0090] In the particular control application relating to FIG. 9,
each of the nodes is preferably housed in a rugged, potted case
made of a suitable lightweight material such as aluminum that
provides environmental protection and allows for heat dissipation,
as previously described with respect to FIG. 4. In other control
environments, other types of housings may be used.
[0091] FIG. 10 is a diagram of a network node 1002 including a node
housing 1005 to which a plug-in module 1012 may be attached. The
network node 1002 may be used in any of the exemplary hierarchical
control networks described previously herein, or in any other type
of control network in which it is required to replace or reprogram
existing network nodes. By use of the plug-in module 1012,
association of a node identifier and/or functional program code
with the network node 1002 may be carried out in a rapid and
convenient manner, without the need for specialized equipment, and
without the possibility of erroneous manual entry of the node
identifier.
[0092] According to a preferred embodiment, as depicted in FIG. 10,
the network node housing 1005 contains the electronics of the
network node 1002, including one or more processors and various I/O
functions. In a preferred embodiment, the electronics within the
network node housing 1005 are similar to that depicted in FIG. 6,
and are described in more detail below with respect to FIG. 11.
With respect to the physical features of the network node 1002
depicted in FIG. 10, the network node housing 1005 includes an
external port 1008 to which the plug-in module 1012 can be
physically attached. In one embodiment, the plug-in module 1012
takes the form of an enclosed cylindrical unit having a cylindrical
module body 1020 containing electrical components. Wrapped about
the periphery of the cylindrical module body 1020, at one end, is a
cylindrical attachment piece 1021 having an inner threading 1025.
The external port 1008 of the network node housing 1005 may take
the form of a relatively short, cylindrically-shaped extension as
shown in FIG. 10, with an outer threading 1007 for receiving the
cylindrical attachment piece 1021. The cylindrical attachment piece
1021 is rotatable, and may be screwed onto the cylindrically-shaped
extension (i.e., external port 1008) to secure the plug-in module
1012 to the node housing, in the manner as is commonly done to
fasten certain types of plastic piping together, for example.
[0093] In one embodiment, the external port 1008 comprises an
arrangement of pins 1006 protruding upwards, emanating from the top
of the external port 1008. The plug-in module body 1020 includes a
matching arrangement of holes 1023 for receiving the pins 1006.
When the plug-in module 1012 is secure fastened to the node housing
1005, the pins 1006 atop the external port 1008 fit snugly into the
holes 1023 along the base of the plug-in module fit 1012.
Alternatively, the pins could be located on the base of the plug-in
module body 1020, while the holes would then be located atop the
external port 1008 on the node housing 1005.
[0094] As further shown in FIG. 10, cables 1030 and 1031 forming a
portion of the continuous, common bus are inserted into the node
housing 1005, to allow the node 1002 to be included as part of a
network such as depicted in any of FIG. 2, 7, 8 or 9, for
example.
[0095] In a preferred embodiment, the plug-in module 1012 contains
a readable memory which, when the plug-in module 1012 is attached
to the node housing 1005, allows electronic interconnection between
the electronics of the network node housing 1005 and the readable
memory. Details of preferred electronics, at a block diagram level,
are illustrated in FIG. 11. As shown therein, a preferred network
node 1102 may comprise many of the same electrical components as
illustrated for the node in FIG. 6. Thus, the network node housing
1105 may contain, among other things, an uplink transceiver 1111, a
downlink transceiver 1121, a CPU 1117 connected to the uplink
transceiver 1111, and another CPU 1122 connected to the downlink
transceiver 1121. Both CPUs 1117, 1122 are preferably connected to
a dual-port RAM 1118, and each CPU 1117, 1122 may be connected to a
ROM program store 1114a and 1124, respectively. The second CPU 1122
is connected through an appropriate interface to I/O ports 1154,
which may comprise sensor inputs, control signal outputs, status
LEDs, LCD display, keypad, or other types of external connections.
It will be understood that the node 1102 of FIG. 11 can have all
the components and functionality of the node 301 shown in FIG. 3;
however, in FIG. 11 only certain components are depicted for the
sake of simplicity.
[0096] Similar to node 603 in FIG. 6, the node 1102 is preferably
capable of both sending and receiving messages (e.g., control
instructions). Typically, the uplink transceiver 1111 operates in a
"slave" mode whereby the node 1102 receives control instructions
using the uplink transceiver 1111 and then responds thereto, and
the downlink transceiver 1121 operates in a "master" mode whereby
the node 1102 issues control instructions (e.g., polls slave nodes)
and awaits a response from other nodes after sending such control
instructions. The downlink transceiver 1121 may be connected to a
secondary data bus, to which may also be connected a plurality of
lower-tier slave nodes.
[0097] The node 1102 may also comprise a pair of switches 1134
connected between the downlink transceiver 1121 and the signal
lines and bus connector 1142, the purpose of which has been
described in detail above with reference to FIG. 6. A timer
mechanism, such as timer 613 accessible to CPU 1117, may be used to
detect a master node failure condition on the main data bus
connected to the bus connector 1142.
[0098] A preferred communication protocol for the node 1102 within
a control network system involves the ability to identify each node
1102 with a unique identifier. Communication between nodes may be
carried out, for example, using half-duplex time division
multiplexing, wherein the master node polls each of the slave nodes
periodically. Each of the nodes is preferably provided with a
unique node identification number or address that distinguishes it
from all other nodes of the control network. The master node sends
a control message to each slave unit in turn, using the node
identification number or address to identify the intended
destination. Each of the slave nodes receives the control message
but only reacts if it recognizes its own node identification number
or address in the control message. The slave node takes the actions
requested by the control message received from the master node.
Within a designated time period after receiving the control
message, the slave node responds to the master node with an
acknowledgment message. Each of the slave nodes are polled in turn
so that the master node can keep track of events happening
throughout the system.
[0099] To facilitate identification of the node 1102, the readable
memory 1114 contained within the plug-in module 1112 stores a
unique node identifier which becomes associated with the node 1102
when the plug-in module 1112 is secured to the module housing 1105.
The readable memory 1114 is defined within the address space of the
node 1102. Once the plug-in module 1112 is connected, the CPU 1117
accesses the node identifier at the address provided for the
readable memory 1114, and uses the node identifier in subsequent
communication activities. The CPU 1117 may, for example, determine
which messages are targeted to the node 1102, and may insert the
node identifier in messages transmitted from the node 1102. The CPU
1117 may share the node identifier with the second CPU 1122 by
loading into the dual-port RAM 1118, at a specified location.
[0100] In addition, the readable memory 1114 may also include
functional program code for the node 1102. The CPU 1117 may be
programmed so that it first attempts to utilize the functional
program code, if any, stored in the readable memory 1114, and if
then secondarily attempts to utilize the functional program code
stored in the program ROM 1114a. The functional program code stored
in the readable memory 1114 may be shared with the second CPU 1122
if desired by downloading it to the dual-port RAM 1118.
[0101] Accordingly, the node 1102 may be programmed or
re-programmed with a unique node identifier and functional program
code simply by connecting or replacing the plug-in module 1112,
avoiding the need to download a node identifier or functional
program code from specialized equipment, and increasing the speed
and convenience by which a node 1102 can be programmed or
re-programmed.
[0102] The readable memory 1114 may contain any type of persistent
data memory, including read-only memory (ROM), programmable ROM
(PROM), or electrically-erasable programmable ROM (EEPROM), for
example.
[0103] FIG. 12 is a conceptual diagram illustrating electrical
connection of the readable memory within a plug-in module to the
electrical components of the node, in accordance with an
alternative embodiment as described herein. The components
illustrated in FIG. 12 are generally analogous to those shown in
FIG. 11. Thus, network node 1202 may comprise a network node
housing 1205 which may contain, among other things, an uplink
transceiver 1211, a downlink transceiver 1221, a CPU 1217 connected
to the uplink transceiver 1211, and another CPU 1222 connected to
the downlink transceiver 1221, operating in a manner similar to
that described for FIG. 11. Both CPUs 1217, 1222 are preferably
connected to a dual-port RAM 1218, and each CPU 1217, 1222 may
optionally be connected to a ROM program store 1214a and 1224,
respectively. The second CPU 1222 is connected through an
appropriate interface to I/O ports 1254, which may comprise sensor
inputs, control signal outputs, status LEDs, LCD display, keypad,
or other types of external connections, as described with respect
to FIG. 11.
[0104] The main difference between the node 1102 depicted in FIG.
11 and the node 1202 depicted in FIG. 12 is that the node 1202
depicted in FIG. 12 has a second electrical connection directly
from the readable memory 1214 of the plug-in module 1212 to the
second CPU 1222, so that the second CPU 1222 can obtain direct
access to the unique node identifier as well as any functional
program code stored in the readable memory 1214. The readable
memory may be partitioned, or may physically comprise two separate
memory chips, to avoid conflicts between the two CPU's 1217 and
1222 in accessing the information stored in the readable memory
1215. In all other respects, operation of the node 1202 of FIG. 12
is essentially the same as the node 1102 depicted in FIG. 11.
[0105] From the standpoint of physical construction, the node
housing 1005 (or 1105 or 1205) may comprise a rugged, potted case
made of a suitable lightweight material such as aluminum that
provides environmental protection and allows for heat
dissipation.
[0106] The plug-in module 1012 (or 1112 or 1212) can take a wide
variety of alternative forms. It may be of any other shape that is
convenient, such as rectangular, square, or polygonal. Likewise,
the external port 1008 may be in the form of an inset, cavity or
depression rather than an extension, with the plug-in module 1012
inserting snugly inside the port. Further, the plug-in module 1012
may be fastened to the node housing 1005 by other suitable means
besides using an encapsulating threaded screw mechanism as shown in
FIG. 10. For example, the plug-in module 1012 may snap into the
node housing 1005, or may have one or more screws externally
attached (similar to many common computer printer cables) to the
plug-in module body 1020, which may be screwed in to corresponding
holes in the node housing 1005. The particular plug-in module 1012
depicted in FIG. 10 provides the advantage of ease of manual
attachment to the node housing 1005, as well as giving a very
secure and stable connection. For applications in which the plug-in
module 1012 needs to be particularly small, a snap-on fastening
mechanism may be preferred.
[0107] While preferred embodiments are disclosed herein, many
variations are possible which remain within the concept and scope
of the invention. Such variations would become clear to one of
ordinary skill in the art after inspection of the specification and
drawings herein. The invention therefore is not to be restricted
except within the spirit and scope of any appended claims.
* * * * *