Communications: electrical – Visual indication – Using light emitting diodes
Reexamination Certificate
2000-09-11
2002-09-10
Wu, Daniel J. (Department: 2632)
Communications: electrical
Visual indication
Using light emitting diodes
C340S870030, C340S870030, C340S002100, C340S003540, C340S003800, C340S315000, C340S315000, C340S315000
Reexamination Certificate
active
06448901
ABSTRACT:
BACKGROUND OF THE INVENTION
Many of today's systems require flexible communication between a number of cooperating electronic nodes or modules, each having a microprocessor and one or more microcircuits. To avoid the need for a large number of individual conductors between each pair of nodes, serial transmission on a single data path is preferred. It is possible to connect each node with every other node, but once there are more than a few nodes, the connections become complex and expensive. For this reason, such connectivity structure is not particularly desirable. A number of communication protocols have been developed to deal with situations having many nodes and high message and data rates. Ethernet and the Internet are just two of the better-known serial transmission protocols having high data and message capacities. Unfortunately, these high capacities come at relatively high cost and complexity as well. These systems have relatively expensive individual nodes with high processing speeds justifying fast (and expensive) internode communication.
For communication systems having a relatively large number of nodes and relatively low message and data rates, it is economical and efficient to use a protocol providing each node with an inexpensive interface circuit. All of the interface circuits are connected to a single conductor pair, so each node can both transmit and receive on this conductor pair. The steadily falling cost of microprocessors and microcircuits generally, allows inexpensively creating such networks having scores or even hundreds of such nodes. One particular form of such a network uses the so-called CAN (controller area network) protocol. The CAN protocol establishes a mechanism for dealing with so-called collisions, which is the situation where a number of nodes transmit simultaneously.
In the CAN protocol, all of the nodes are connected to a single conductor pair. Data is transmitted from one node to all of the others in messages carried serially on the conductor pair. The messages are binarily encoded in the voltages on the conductor pair. Each message has a leading ID code that uniquely identifies the message, followed by a number of other fields of assigned length. The information in these fields includes the message length and the data itself. The CAN protocol uses hardware that treats one of the voltage levels assigned to one of the binary bit values as what is called dominant, the other recessive. Should two or more nodes transmit simultaneously causing colliding messages, a dominant voltage level transmitted by any node causes the conductor pair to carry a dominant voltage level during that time regardless of the number of other nodes simultaneously transmitting a recessive level. Each node monitors the signals carried on the conductor pair at all times. The nodes are programmed to transmit messages with prearranged ID codes.
Each node is programmed to continuously sense the message traffic on the conductor pair. When a node is not transmitting and detects in a message, an ID code to which it is programmed to respond, the node receives the message following and responds appropriately. While a node is transmitting, it continues to sense the signals on the conductor pair. When a node, during a bit time, is transmitting a recessive voltage and senses voltage signal carried on the conductor pair is dominant that means that a message collision is occurring, and the node transmitting the recessive voltage signal ceases transmitting. If two or more nodes are transmitting dominant voltage levels simultaneously, it may take several bit times before all of the collisions have been resolved. By assigning unique (to that node) leading ID, codes for all of the messages sent by all of the nodes, eventually every node but one will detect a difference between its transmitted signal voltage and the conductor pair signal, leaving just that one node to transmit the remaining portion of its message. U.S. Pat. Nos. 5,001,642 and 5,303,348 describe the CAN protocol in more detail.
One advantage of the CAN protocol is the possibility for providing power conductors that many nodes can share. For example, the CAN protocol as originally conceived allows a pair of DC power conductors to be routed to each node along with the data conductors. It may even be possible in certain systems for data and power to share one or more common conductors. Thus, a four or even three wire bundle connecting all of the nodes can provide both power and communication for them.
As mentioned, some of these systems may have a large number of nodes. Miswiring during system assembly, or operational defects of an individual node after installation, creates a significant failure diagnosis problem. When reduced capability node hardware is involved, there is less opportunity for node assisted diagnosis of node and system operating status. There may not be any sort of device in the node allowing human input signaling status of the nodes or changing node operation to assist trouble-shooting. Test instruments can detect failures in individual nodes of course, but this may require that the node be detached from the system, and of course requires either having a tester handy or calling a technician.
On a different point, certain distributed control systems, for example those used to control HVAC systems, have very low data rate requirements. Traditionally, these systems are designed to operate, in the U.S. anyway, with 60 Hz., 24 v. AC power. Conventionally, control elements such as thermostats, burner controls, and humidistats control the switching of power to the remotely sited air conditioners, furnaces, humidifiers, and blowers of the HVAC system.
BRIEF DESCRIPTION OF THE INVENTION
We have developed a unique system employing certain principles of CAN architecture. This unique system provides advantages over the conventional system structure and yet easily integrates with a conventional and existing system. A number of novel features in this unique system assist in achieving this easy integration and enhance operation relative to these existing systems.
One of these features allows each of the nodes in the system to receive operating power from low voltage AC power, and at the same time use the 50 or 60 Hz. AC waveform for synchronizing the start of each bit interval for each node. In one embodiment, the two zero crossings of the power waveform per cycle synchronize the starts of 100 or 120 bit intervals each second. Such a system has a plurality of nodes for communicating with each other through messages encoded in a data signal comprising a series of data bits sent and received on a data line respectively to and from a data terminal of each node connected to the data line. The data bits are encoded in dominant and recessive. signal levels corresponding to binary values and by which each said node resolves collisions of messages sent by more than one node. Each said node receives an AC waveform at an AC power terminal from an AC power line.
Each node includes a power supply for providing DC power at first and second DC power terminals for operating the node and for communicating through the data line with the other nodes. The second DC power terminal voltage level corresponds to the dominant signal level. Each node has an interface circuit comprising i) a pull-up impedance connected between the first DC power terminal and the node's output data terminal, and ii) a variable impedance connected between the node's output data terminal and the second DC power terminal. Each interface circuit has a control terminal. The variable impedance in each interface circuit provides a first impedance value substantially smaller than the pull-up impedance value responsive to an output data signal at the control terminal having a first level, and an impedance substantially larger than the pull-up impedance value responsive to a second level of the output data signal at the control terminal. The variable impedance's first impedance value holds the data line voltage level substantially at the dominant sig
Adams John T.
Nichols Steven C.
Honeywell International Inc
Nguyen Tai T.
Wu Daniel J.
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