Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Signal transmission integrity or spurious noise override
Reexamination Certificate
1999-11-29
2003-10-21
Nguyen, Minh (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Signal transmission integrity or spurious noise override
C327S141000, C327S518000, C714S731000
Reexamination Certificate
active
06636100
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a CAN controller and a one-chip computer having the built-in CAN controller, each of which enables the operation test thereof to be executed stably at a high speed. More particularly, this invention relates to a CAN controller and a one-chip computer having the built-in CAN controller, each of which only when the operation test thereof is performed is prevented from being influenced by the operation of its re-synchronizing function.
BACKGROUND OF THE INVENTION
With a recent spread of personal computers, establishment of a network build-up technology such as a client server system, and complete arrangement and adjustment of a communication infrastructure, the introduction of a network computing has proceeded not only on an enterprise level but also on a person level. The network computing that is represented by the Internet or a LAN (Local Area Network) in general is mainly intended to perform the exchange of information between people smoothly and over a wide range.
Also, in the field of industry, in a FA (Factory Automation), etc., the pieces of control equipment that have been functionally dispersed and had their dispositions dispersed are conventionally being unitarily controlled and managed by a network to thereby achieve the optimization of the production activity. For example, attention has been drawn toward a CIM (computer integrated manufacturing system) as a computer system that inclusively unifies individual technical data pieces and production data pieces such as a CAD (computer-aided design), CAM (computer-aided design), CAE (computer-aided design), assembling, and examination, and further even a production plan and production management.
It is very useful to introduce the network computing, in this way, with respect to the operations that are to be performed under a common object or common circumstances, especially, with respect to the processing form in which the cooperative operations are needed between a plurality of equipment pieces. In this view, even in case of the automobiles, the added value and function of which have yearly been increased, there has been demanded a system that unitarily controls and manages respective electrified units, which have been electronically controlled, through a network. Especially, the introduction of a CAN (Controller Area Network) that is an on-vehicle LAN standard has proceeded.
The CAN is a protocol that has been internationally standardized as an ISO 11898. It adopts a serial communication system that replaces a differential voltage between two lines called “CAN buses” with a digital value of 0/1 and that uses the resulting signal as a transmission and reception signal. It therefore has a high resistance to noise and makes it possible to set its transmission rate up to 1 Mbps at maximum. It therefore characteristically enables a very highly reliable and highly speedy network control to be performed even when compared to the conventional communication system.
Ordinarily, a CAN controller is loaded on each of the above-described respective electrified units (each hereinafter called “a CAN node”) that have been connected to the CAN buses. The data transmission and reception between the CAN nodes that are made through the use of the CAN buses as an intermediary can be performed with this CAN controller. Especially, the CAN controller characteristically has an abnormality detecting function on the network and a re-synchronizing function thereon to thereby achieve the stabilization of the communication.
Further, the CAN is a bus system that has multi master ability. Therefore, every CAN node can transmit data onto the CAN buses and a plurality of CAN nodes can receive the signal on the CAN buses simultaneously. In this CAN network, it is not necessary, in principle, to set a so-called “apparatus address” (“station ID”). Instead, the content of the message is represented by an ID (a message ID) that has been added to each piece of message data to be transmitted.
This message ID is also referred to when determining the priority when bus accesses from a plurality of CAN nodes have competed. Only the message from the CAN node that has won a victory out of the communication mediation as a result of the line scramble appears on the buses. And the CAN controller that has been loaded on each CAN node determines according to this message ID whether or not the message should be formally taken in.
Ordinarily, the CAN controller is supplied in the form of a chip so as to exhibit the function that has been included therein in accordance with the CAN protocol. It therefore serves as an interface between the CPU that is loaded on the CAN node and the CAN buses. Further, by making this CAN controller into a module, the CAN controller is also supplied in actuality in the form of a one-chip microcomputer having the CAN controller built-in.
The CAN is originally developed for the purpose of being used in an automobile as mentioned above. However, by taking advantage of the characterizing features thereof that the amount of wiring is reduced; the weight and cost are resultantly reduced; the real-time performance is high; and the strength against the electrical interference is high, the CAN is also adopted in the built-up of the above-described FA, medical equipments, or ships.
In the above-explained CAN controller or one-chip microcomputer (hereinafter called “a CAN chip”) having the CAN controller built-in, the signal is delayed due to the signal processing circuits disposed between the CRX terminal that receives a serial signal from the CAN buses and the CAN module that is actually exhibitive of various kinds of their functions that have been included therein in accordance with the CAN protocol. Therefore, the signal that is received by the CAN module is delayed with respect to the signal received in the CAN buses. In addition, there is a delay that occurs due to the transmission cable from the transmission node to the reception node. The above-described re-synchronizing function operates in order to compensate for these signal propagation delays.
However, in the manufacturing process of the above-described CAN chip, when testing the operation of the CAN module section, the above-described delay in the signal propagation fluctuates depending on the testing conditions such as the environmental temperature and the applied voltage, and, according to each of these fluctuations, the re-synchronizing function is inconveniently executed. Therefore, there is the problem that the stable and speedy test in a stationary state of synchronization was inconveniently hindered.
This problem involves therein the possibility that, especially, with respect to a normal CAN chip, the test result indicating that a CAN chip is defective may inconveniently be output even in a case where a serial testing signal is input to an input terminal (hereinafter called “a CRX terminal”) having a serial signal input thereto from the CAN buses with a timing that is determined on a basis of, for example, an internal clock signal.
It is indeed possible to prepare test vectors for each fluctuating testing condition and repeat a test that corresponds to each of such test vectors. However, such test vectors become huge in number. On the other hand, it is difficult to predict or estimate the fluctuation of the testing conditions. Therefore, this solution is not a realistic one.
The above-described problem will be explained with reference to the drawing.
FIGS. 5A and 5B
are explanatory views illustrating the occurrences of a bit timing in the conventional CAN controller. Especially,
FIG. 5A
illustrates the exhibition of the re-synchronizing function with respect to first testing conditions while
FIG. 5B
illustrates the exhibition of the re-synchronizing function with respect to second testing conditions.
In the CAN, a length of time that is called “a bit time” is allotted to each of the respective bits that constitute the above-described message (message frame). This bit time is constructed of four segments of a Synchronizatio
Burns Doane , Swecker, Mathis LLP
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Minh
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