JP4905808B2 - Serial communication network system - Google Patents

Description

  The present invention relates to a serial communication network system.

JP-A-61-81235 JP 7-42609 A JP 7-42609 A

  In recent years, many safety and comfort functions are installed in automobiles, and ECUs (electronic control units) that control these individual functions are connected via an in-vehicle network to perform cooperative operation. A typical example of such an in-vehicle network is a CAN (Controller Area Network), which is widely adopted as a standard serial communication network for powertrain, chassis, body, and information systems. CAN is a multi-master serial communication protocol that can handle relatively high transmission rates, and is asynchronous (start-stop synchronization), but realizes high-accuracy node synchronization such as resynchronization processing by edge detection and bit stuffing. is doing. In order to increase the noise margin, a differential transmission method using twisted pair wires is adopted, and in order to realize highly reliable multi-master communication such as bus arbitration and bus state transition using an error counter, Various ideas have been made.

However, the above-mentioned features of CAN also have a side where network costs are likely to rise. For example, among body equipment classified as body systems, high-speed and detailed control such as electric door mirrors and power windows is possible. As a network for device control that is not so required, there is a drawback that it tends to become excessive specifications. Therefore, in order to make up for this drawback, LIN (Local Interconnect Network) has been proposed as a simple serial communication network, and actual implementation is progressing. Like CAN, LIN is asynchronous (start-stop synchronization), but is a single master system, and in response to this, half-duplex UART (Universal Asynchronous Receiver)
In addition to a simple hardware configuration such as a node configuration by Transmitter) and a single-wire bus, a synchronization frame is incorporated into the header that makes up the master task, and a simple synchronization protocol that corrects the slave baud rate by referring to the reference waveform for time correction. By adopting, although the transmission rate is low, a significant cost reduction can be realized as compared with CAN.

  By the way, in LIN, conventionally, there are many cases in which device control is performed only by master / slave communication, that is, all control is constructed in such a manner that data from the slave node is returned as a response only to the master node. It was. For example, when it is desired to drive and control the target device with reference to the detection value of the sensor, the sensor control slave node sends the sensor detection value as data (response) to the master node, and the master node acquires the detection value. In the next task (header), the target device to be controlled is designated. For example, in the case of simple control that switches the car navigation screen to the back monitor according to the shift position, the master node may determine whether to switch the monitor according to whether the shift position sensor is “reverse”. There was no need to send the shift position sensor information directly to the slave node that performs switching control.

  On the other hand, depending on the form of control, it may be advantageous to transmit the data not to the master node but to a slave node different from the transmission source. For example, when performing control to change the sonar output form (for example, ringing interval) in multiple stages or continuously according to the distance detected by the obstacle sensor, if the control is to be performed only by communication between the master and slave, Sonar operations with different ringing intervals according to sensor detection values must be handled as individual tasks, which is very troublesome. However, if the sonar control slave node is configured to directly acquire the sensor detection value from the sensor control slave node and voluntarily determine the sonar ringing interval, the control is greatly simplified. In this case, data (sensor detection value) transfer from the sensor control slave node to the sonar control slave node, that is, communication between the slave and the slave is performed.

  When performing communication between slaves / slave, the following method can be adopted as a procedure for matching with the LIN protocol. That is, a header having a synchronization field and an ID field is sent to the communication bus. The header is received by all slave nodes, and each slave node refers to the scheduling table stored in the ROM or the like, and checks whether the ID written in the header designates itself as a transmission node or a reception node. Check. If the transmission node is designated, data uniquely designated by the ID is sent as a response to the communication bus. On the other hand, if it is designated as a receiving node, it receives a response from the transmitting node containing the data. In other words, since the response from the sending node is sent not only to the master node but also to all other slave nodes at the same time, it is directed to the master node by recognizing that it is the receiving node by the header ID. It is possible to receive data in the form of intercepting the response (in addition, an ID specifying the receiving node is separately incorporated in the header, and the receiving node is dynamically determined each time data is transmitted. ).

  As described above, in the LIN, every time data transmission is performed, the slave node corrects the baud rate according to the time correction reference waveform from the master node, and synchronizes. In particular, when communication between in-vehicle ECUs (nodes) is performed using UART, it is only in one data unit (if the data width is 8 bits, a total of 10 bits including start bit and stop bit for start-stop synchronization). Since synchronization is not possible, particularly strict accuracy is required for the baud rate (for example, ± 1.0% for ISO 9141).

  Here, if only master-slave communication is used, the oscillation accuracy of the master node that determines the transmission clock pulse width (that is, the stability of the reference waveform for time correction using the master node) is stably secured. Therefore, the slave node that measures this can adjust the down-conversion ratio in accordance with the stable transmission clock of the master node each time, even if the oscillation frequency on the slave side fluctuates (for example, due to temperature characteristics). Synchronization accuracy can be ensured. Therefore, in anticipation of this, the master node employs a high-precision oscillation circuit such as crystal or ceramic, while the slave node oscillation circuit is configured at a low cost by a CR oscillator or the like.

  However, when the slave / slave communication is performed, the response from the transmission slave node is transmitted at a baud rate that matches the master node with the oscillation frequency of the transmission slave node as a reference. On the other hand, the receiving slave node receiving this receives this by the baud rate adapted to the master node with reference to the oscillation frequency of the receiving slave node. At this time, if there is a non-negligible difference between the oscillation accuracy of the transmission slave node and the oscillation accuracy of the reception slave node, a large deviation occurs in the baud rate between the transmission side and the reception side, and the required synchronization accuracy is reduced. There is a problem that cannot be satisfied. In particular, this problem becomes more serious when the oscillation circuit of the slave node is configured with a low-cost but low-oscillation circuit such as a CR oscillator as described above.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a serial communication network system capable of ensuring the synchronization accuracy at the time of communication between slaves / slaves without problems in single master type serial communication in which baud rate correction is performed using a reference waveform for time correction. .

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, the serial communication network system of the present invention is:
A serial communication network system comprising one master node and a plurality of slave nodes connected by asynchronous serial communication,
A master time correction reference waveform sending means for sending a master time correction reference waveform reflecting the baud rate of the master node to the serial communication bus when the master node performs communication between the slave node and the master / slave;
Slave time correction that is provided in each slave node and sends a slave time correction reference waveform that reflects the baud rate of its own slave node to the serial communication bus when communicating with other slave nodes that are communicating with each other. Reference waveform sending means,
Baud rate correction means provided in each slave node, for correcting the baud rate of the slave node based on both the master time correction reference waveform acquired from the master node and the slave time correction reference waveform acquired from the other slave node; , Provided.

  According to the above configuration, when performing slave-slave communication, the slave node acquires time correction reference waveforms from not only the master node but also the slave node that is the communication partner, and these master time correction reference waveforms. Since the baud rate of its own slave node is corrected based on both the slave time and the reference waveform for slave time correction, baud rate correction between slave nodes, which was not considered at all in the past, is now possible. Synchronization accuracy can be secured without problems.

  INDUSTRIAL APPLICABILITY The present invention is particularly preferably applicable to a LIN communication network that is particularly widespread as an in-vehicle communication network or the like as a single-master asynchronous serial communication network (in this case, the serial communication bus is a LIN communication bus). Become). While following the advantages of LIN communication already explained in the background art, baud rate correction at the time of slave / slave communication, which was impossible with conventional LIN communication, is possible, and the use of communication between slave / slave is expanded. It can also contribute to the diversification of network control related to in-vehicle functions.

  The master node may be provided with a master oscillation circuit that generates a master reference clock signal and a master transmission clock signal generation circuit that generates a master transmission clock signal by down-converting the master reference clock signal. Each slave node includes a slave oscillation circuit that generates a slave reference clock signal having a frequency corresponding to the master reference clock signal, and a slave transmission having a frequency corresponding to the master transmission clock signal by down-converting the slave reference clock signal. A slave transmission clock signal generation circuit for generating a clock signal is provided. The master reference clock signal and the slave reference clock signal provide operation clocks of the CPUs that are the master node and the slave node, respectively, and are set in a range of, for example, about 1 MHz to 100 MHz (for example, 24 MHz) in in-vehicle communication. On the other hand, the master transmission clock signal and the slave transmission clock signal are generated by down-converting the above-mentioned reference clock signal from a hundredth to a thousandth frequency, and the baud rate is, for example, in the case of LIN communication. From 0.5 kbps to 20 kbps at the maximum.

The baud rate correction means provided in each slave node can be specifically configured as having the following requirements.
Master baud rate measuring means: measures the baud rate of the master node indicated by the master time correction reference waveform using the slave reference clock signal (of its own slave node). Specifically, the clock pulse width of the master time correction reference waveform (time interval between adjacent pulse edges (one rising edge and the other falling edge)) is measured by a timer using a slave reference clock signal. This mechanism is also used in the conventional LIN communication.

Slave baud rate measuring means: The slave baud rate of the slave node that is the communication partner indicated by the slave time correction reference waveform is measured using the slave reference clock signal. More specifically, the clock pulse width of the slave time correction reference waveform sent from the communication partner (where the reciprocal corresponds to the baud rate) is similarly measured by the timer using the slave reference clock signal. There is an advantage that the baud rate measurement of the slave node can be carried out with almost the same configuration as the baud rate measuring means (of course, there is an advantage that the hardware and software for timer measurement can be shared with the master baud rate measuring means).

  The baud rate of the slave node is corrected by referring to both the measurement result of the baud rate of the master node and the measurement result of the baud rate of the slave node that is the communication partner. Can be reduced. Specifically, the master baud rate measuring means and the slave baud rate measuring means can respectively measure the clock pulse widths of the master time correction reference waveform and the slave time correction reference waveform, and the baud rate correction means can be used for master time correction. The baud rate of the slave node can be corrected based on the average value of the clock pulse width of the reference waveform and the clock pulse width of the reference waveform for slave time correction. The average value may be an arithmetic average or a geometric average, and an average may be calculated by appropriately weighting the measured values of the clock pulse widths of the master and slave. .

  Note that the greater the down-conversion ratio of the slave reference clock signal, the higher the quantization level for measuring the pulse width of the master transmission clock signal and the slave transmission clock signal. Further, the slave oscillation circuit can be configured by an oscillation circuit with lower oscillation accuracy (that is, less expensive) than the master oscillation circuit. For example, the master oscillation circuit can be constituted by a crystal oscillation circuit or a ceramic oscillation circuit, and the slave oscillation circuit can be constituted by a CR oscillation circuit.

  In LIN communication, a message frame structure for data transmission is defined by a protocol, and a slave time correction reference waveform unique to the present invention must also be incorporated into a message frame within a range consistent with the LIN protocol. As described in the background art, the LIN communication is a single master system, and one of a plurality of slave nodes is set as a transmission slave node, and the other one or more is set as a reception slave node to transmit data from the transmission slave node to the reception slave node. At that time (that is, when communicating between slaves / slave), the communication itself has a protocol agreement that always starts from transmission of a header as a master task.

  Specifically, in the LIN communication, the master node has a break field indicating the start of a message, a master synchronization field incorporating a master time correction reference waveform, and a slave node specification field (ID field) for specifying a data transmission slave node. And a header sending means for sending a header arranged on the communication bus. Each slave node has header receiving means for receiving a header, and receives this header and returns a response as a slave task to the master node.

  As described above, the header is received by all the slave nodes, and each slave node confirms whether or not its own node is designated as a (data) transmission node in the slave node specification field. If the transmission node is designated, the data is sent as a response to the communication bus. Although this response is originally directed to the master node, the contents of the response sent on the communication bus can be seen by any slave node, so the slave node designated in advance as the receiving node intercepts this response. can do. Therefore, it is most appropriate to place the slave time correction reference waveform used for baud rate correction between the slave and slave at the head of the response. In other words, the response sending means provided in the slave node is the transmission target when the slave slave field is designated as the transmission slave node indicated by the slave node identification field and the slave synchronization field incorporating the slave time correction reference waveform. A response in which a data field in which data is incorporated and an error check field are arranged may be sent to the communication bus. Conversely, in LIN communication to which the concept of the present invention is applied, one of the major features is that a slave synchronization field is newly added at the head of the response.

  When the difference in the oscillation accuracy of the slave oscillation circuit provided in each slave node is large (for example, when the specification of the slave oscillation circuit is different between nodes, or even if it is the same specification, it is greatly affected by variations between lots, etc. For example, the baud rate correction at each slave node using the slave time correction reference waveform can be corrected by statistically taking into account the measurement result of the slave time correction reference waveform received in the past. / The synchronization accuracy between slaves can be further improved. On the communication bus, every time a communication event occurs, a response is continuously sent from one of the slave nodes. As described above, whether the response and the slave time correction reference waveform included in the response are involved in the communication event. Regardless of whether it is present or not, any slave node can intercept it. Therefore, each slave node acquires a reference waveform for slave time correction included in response to an event that is not designated as a transmission node or a reception node, and transmits a transmission clock pulse width (the reciprocal is a baud rate). It is also possible to use the measurement result to correct the transmission clock pulse width of the own node. However, in this method, if the difference in oscillation accuracy between slave nodes is large, the slave node that is not involved as the communication partner of the local node is unnecessarily affected by the oscillation accuracy, and slave / In some cases, the synchronization accuracy between slaves cannot be sufficiently improved.

  Therefore, the baud rate measurement result value storage means for storing the actual values related to the baud rate measurement results of the master node and the slave node that are communication partners in the baud rate correction means in each slave node in association with the information that identifies the communication partner. The baud rate measurement result value stored in the baud rate measurement result value storage means is selectively read out corresponding to the current communication partner, and the baud rate of the slave node is corrected based on the baud rate measurement result value. Can be configured to. If only the baud rate measurement result value of the slave node corresponding to the current communication partner is selected and reflected in the baud rate correction of the own node, it is natural that the oscillation accuracy of the slave node not involved as the communication partner of the own node is improved. The influence can be eliminated and the correction accuracy can be increased.

  For example, in each slave node, the baud rate correction means, when the slave node is designated as a reception slave node by the master node, is stored in the baud rate measurement result value storage means, and the slave on the master node and the transmission side The baud rate of the slave node can be corrected based on each baud rate measurement result value related to the node. The baud rate measurement result value is updated using the latest measurement values of the master baud rate and slave baud rate. By adding past measurement results to the latest measurement values of the master baud rate and slave baud rate, it is possible to reduce the influence of measurement errors and variations, or environmental errors such as measurement temperature, and improve baud rate correction accuracy.

  On the other hand, in each slave node, when the own slave node is designated as a transmission slave node, the baud rate correction means performs baud rate measurement results for all the nodes that are transmission partners of the master node and the slave node. It is also possible to read out from the actual value storage means and correct the baud rate of the slave node based on the baud rate measurement actual value. When the own node becomes a transmission slave node, the node becomes an output source of the slave time correction reference waveform, so there is no room for using a new baud rate measurement result at the communication event for correction. However, if the past baud rate measurement result when the communication partner becomes the transmission node is stored as the actual value, the baud rate can be corrected even when the own node becomes the transmission slave node using this, and the correction accuracy It can contribute to improvement.

  The baud rate correction means in each slave node is provided with a baud rate measurement result value storage means for storing the actual values related to the baud rate measurement results of the master node and the slave node as communication partners without distinguishing the communication counterpart, and the baud rate measurement result value The baud rate measurement result values of all nodes other than the own slave node stored in the storage means may be read out, and the baud rate of the own slave node may be corrected based on the baud rate measurement result values. This method is not desirable when the difference in the oscillation accuracy of the slave oscillation circuit is large, but if the specification of the slave oscillation circuit is uniform and the influence of lot variation is small and the oscillation accuracy is relatively uniform, A good baud rate correction effect can be achieved, and the actual value related to the baud rate measurement result is adopted without distinguishing the communication partner, so that the correction method is simplified and the software development man-hours can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the overall configuration of the serial communication network system of the present invention. The serial communication network system 1 is a system in which one master node 10 (M) and a plurality of slave nodes 10 (S) are connected by a LIN communication bus 20 and constitute a body-based in-vehicle network. Each node 10 is composed of a microcontroller IC incorporating a half-duplex URAT, and is connected to a LIN communication bus 20 composed of a single metal wire via a transceiver IC 11.

  FIG. 2 is an internal block diagram of a microcontroller IC constituting each node. The microcontroller IC mainly includes a microprocessor 101 including a CPU, a RAM, and a ROM, and a URAT integrated circuit 110 that forms a part of the peripheral of the microprocessor 101. The protocol part of LIN communication (including a program for baud rate correction described later) is stored in the ROM of the microprocessor 101. On the other hand, the URAT integrated circuit 110 is connected to the microprocessor 101 by a bus 102, and receives a reception register 103, a transmission register 104, an oscillation circuit 105, a frequency dividing circuit 106, a reception circuit 107, a transmission circuit 108, and a timer counter 109 for baud rate measurement. It is what has.

  Although the basic block of the microcontroller IC itself is not different between the master node and the slave node, the master node 10 (M) is composed of the crystal oscillator circuit 105Q (or ceramic oscillator circuit 105C). On the other hand, the slave node 10 (S) has a difference constituted by the CR oscillation circuit 105CR. The reference clock signal from the oscillation circuit 105 (master reference clock signal in the case of a master node, slave reference clock signal in the case of a slave node; both are set in a range of 1 MHz to 100 MHz (for example, 24 MHz)) While being input to the processor 101 as an operation clock signal, the frequency dividing circuit 106 down-converts it to a frequency (0.5 to 20 kHz (for example, 10 kHz (9600 bps)) corresponding to an instruction value from the microprocessor 101. It is distributed and input to the receiving circuit 107 and the transmitting circuit 108 as a transmission clock signal for serial communication.

  In LIN communication, a message frame structure for data transmission is defined by a protocol. FIG. 3 is a conceptual diagram showing the message frame structure employed in the present invention in comparison with the conventional example. The message frame includes a header HD and a response RSP. The header HD operates as a master task, and the response RSP operates as a slave task.

  The header HD includes a break field BF indicating the start of a message, a master synchronization field SF (MS) incorporating a master time correction reference waveform, and a slave node specification field (hereinafter, referred to as a data transmission slave node 10 (S)). IDFs (also called ID fields) are arranged in this order. On the other hand, the response RSP is conventionally composed only of a data field DF in which data to be transmitted is incorporated and an error check field (specifically, a chuck sum field for transmitting a checksum) CSF. In the embodiment of the present invention, a slave synchronization field SF (SS) for transmitting a slave time correction reference waveform is newly added before the data field DF, that is, at the head of the response RSF.

  The contents of the header HD by the master node 10 (M) and the contents of the response RSP by the slave node 10 (S) are temporarily stored in the transmission register 104 from the microcomputer 101 and transmitted from the transmission circuit 108. These are received by the reception circuit 107 at the reception node, and the contents are read by the microcomputer 101 via the reception register 103.

  The data width transmitted at one time by the data field DF is, for example, 8 bits, and start bits and stop bits for start / stop synchronization are added to the front and back, for example, a total of 10 bits becomes one data unit. However, the data width can be variably set. When communication between nodes is performed using UART, only one data unit can be synchronized. Therefore, for baud rate, for example, ISO 9141 requires ± 1.0%, and particularly strict accuracy is required.

  In the master synchronization field SF (MS), a master time correction reference waveform reflecting the baud rate of the master node 10 (M) when the master / slave communication is performed with the slave node 10 (S) is transmitted (master time). Correction reference waveform sending means). In the slave synchronization field SF (SS), when the slave / slave communication is performed between the two slave nodes 10 (S), the slave time reflecting the baud rate of the own slave node 10 (S) (transmission slave node). A correction reference waveform is sent to the serial communication bus (slave time correction reference waveform sending means). Each slave node 10 (S) corrects the baud rate of its own slave node 10 (S) based on both the master time correction reference waveform and the slave time correction reference waveform (baud rate correction means).

  In the master synchronization field SF (MS) and the slave synchronization field SF (SS), each time correction reference waveform has a fixed number of bits as shown in FIG. 9 by the master transmission clock signal and the slave transmission clock signal, respectively. Generated as a clock pulse waveform. In FIG. 9, 9 bits A to H are determined as clock pulse width measurement targets, and the first bit A is also used as a start bit, and is not used for measurement after the last bit I. A stop bit follows. Note that only 8 bits B to H excluding the start bit A may be measured.

  The clock pulse width is measured as shown in FIG. 10 by a timer counter 109 (which may be configured as a dual counter) that counts up with a master reference clock signal or a slave reference clock signal. The dominant level section and recessive level section that are continuous on the waveform are measured, and the first timer starts counting using the edge indicating the section start position as a trigger, and ends counting upon receiving the edge indicating the section end position. . The edge is used both as a command signal for reading the count value of the first timer to the microcomputer and as a trigger for starting the counting of the second timer, and the counting of the next section is similarly performed by the second timer. The counting ends at the edge position indicating. The edge again triggers the first timer, and the same operation is repeated. Each of the first timer and the second timer sends a reset signal to the other timer at an appropriate timing after the start of counting.

  In LIN communication, a communication event is always started from the master node. As shown in FIG. 7, the master node MN sends the header HD to the communication bus 20 (header sending means). The communication bus 20 is a single wire, and the header HD sent on the communication bus 20 is in a state where it can be seen from all the slave nodes SN, that is, in a receivable state. Each slave node 10S that has received the header HD measures the clock pulse width in the waveform while receiving the master time correction reference waveform of the master synchronization field SF (MS) (regardless of the reception / transmission node) For example, the average of these values is calculated as a value reflecting the master baud rate (hereinafter also referred to as “calculating the baud rate”).

  The master reference clock signal and the slave reference clock signal are set to the same target oscillation frequency, and the clock pulse width measurement value of the master time correction reference waveform is the reference measurement value when the target oscillation frequency is counted. Is stipulated. However, if there is an error variation in the slave reference clock signal, the measurement value of the clock pulse width deviates from the reference measurement value. Therefore, the deviation of the microcomputer 101 of the slave node 10 (S) involved in communication in FIG. 2 is reduced. Thus, the clock pulse width of the own node is corrected and calculated, and the frequency instruction value corresponding to the correction result is output to the frequency dividing circuit 106. In response to this, the frequency dividing circuit 106 changes the down-conversion ratio to the instructed frequency and corrects the slave baud rate. Details of the correction calculation will be described later.

  Next, an identifier (ID) is described in the ID field IDF, and a communication event and, consequently, a slave node involved in the communication event is uniquely specified according to the content of the identifier. Specifically, a scheduling table as shown in FIG. 4 is stored in the ROM of each slave node SN, and a transmission slave node (and transmission data) and a reception slave node are specified for each identifier content. Information is stored in a uniquely associated form.

  Each slave node 10 (S) refers to the scheduling table and confirms whether the identifier (ID) designates the own node as a transmission slave node. If it is designated as a transmission slave node, data requested by the identifier is sent as a response to the communication bus (response sending means). On the other hand, the header is also transmitted to the receiving slave node 10 (S) R, and it can be confirmed here that the own node is the receiving slave node with reference to the scheduling table. The response from the transmission slave node 10 (S) T is originally directed to the master node 10 (M), but the content of the response sent on the communication bus is visible from any slave node 10 (S). Therefore, the receiving slave node 10 (S) R can receive data in the form of intercepting this response. In this way, data communication between slaves / slave is established.

  In the system of the present invention, the transmission slave node 10 (S) T generates a slave time correction reference waveform by down-converting its slave reference clock signal, and as shown in the lower part of FIG. The response RSP is sent in the form of adding it to the head as the synchronization field SF (SS). Prior to receiving the data field DF, the receiving slave node 10 (S) R receives this slave synchronization field SF (SS), and in the same way as in the case of the reference waveform for master time correction described above, Each clock pulse width is measured, and for example, an average value of these is calculated as a clock pulse width reflecting the baud rate of the transmission slave node. On the other hand, the receiving slave node 10 (S) R also receives the header HD before receiving the response RSP, and refers to both the baud rate of the master node measured at that time and the baud rate of the transmitting slave node measured at the time of receiving the response. The baud rate of the own node is corrected.

  That is, when performing slave-slave communication, time correction reference waveforms are acquired not only from the master node 10 (M) but also from the transmission slave node 10 (S) T, and these master time correction reference waveforms and slaves are acquired. Since the baud rate of the slave node 10 (S) is corrected based on both the time correction reference waveform, the baud rate correction between the slave nodes 10 (S), which has not been considered in the past, can be performed. Synchronization accuracy during inter-communication can be ensured without problems. In addition, if a method for storing the past baud rate measurement values and correcting the baud rate using the actual values as described later is adopted, a slave time correction reference waveform cannot be acquired from another node at the current communication event. The baud rate can also be corrected at the transmission slave node 10 (S) T.

  Hereinafter, the baud rate correction method in the slave node will be described in more detail. Each slave node (SN1, SN2,...) Measures the clock pulse width of the master time correction reference waveform every time it receives a header from the master node, and this is measured by the master node (MN) as shown in FIG. The baud rate measurement result result value is stored in a result value memory in the RAM (baud rate measurement result value storage means). Also, when becoming a receiving slave node, measure the clock pulse width of the reference waveform for slave time correction included in the response from the receiving slave node, and specify the receiving slave node using this as the measurement result actual value of the slave baud rate Corresponding to the information (SN2, SN3,...) Is stored in the result value memory in the same manner.

As shown in FIG. 5, the measurement value value of the clock pulse width is accumulated in the actual value memory for a certain past number of times (five times in FIG. 5) for each transmission source node of the time correction reference waveform. . FIG. 5 schematically shows the contents of the actual value memory of the slave node SN1, for example, the baud rate (clock pulse width) measurement actual values from the master node MN are f ¹ _m1 , f ¹ _m2 , and f ¹ , respectively. _m3, ‥, ^f ₁ 21 baud rate from the slave node SN2 (clock pulse width) measured actual values, _{^{respectively, f 1 22, f 1 23}} , ‥, stored in the shift memory form as such. Then, the average value (f ¹ _mn , f ¹ _2n , f ¹ _3n ...) Of the accumulated measurement performance values for each transmission source node is calculated as information reflecting the current baud rate of each transmission source node. It is stored according to the memory. When a new time correction reference waveform is received from each transmission source node, the latest baud rate measurement actual value of the transmission source node is measured, and the oldest actual measurement value stored is erased, and the latest measurement actual value The average value reflecting the above is recalculated, and the stored contents of the result value memory are updated.

  FIG. 8 shows an example of a processing flow of baud rate correction in the microcomputer 101 (FIG. 2) of each slave node. In S1, it is confirmed whether or not the master synchronization field (header) is received. If received, the process proceeds to S2, and the master baud rate (clock pulse width) is measured by the above-described method, and the result value memory of FIG. Store and update the average value. On the other hand, if the master synchronization field has not been received, S2 is skipped. Next, in S3, it is confirmed whether or not the ID field is received. If it has been received, the process proceeds to S4, and with reference to the scheduling table of FIG. 4, it is confirmed whether or not the identifier (ID) in the ID field designates the own node as a transmission slave node. If the own node is designated as a transmission slave node, the process proceeds to S5, similarly, referring to the scheduling table, identifies which reception slave node is (possibly a plurality of), and proceeds to S6.

In S6, referring to the actual value memory of FIG. 5, all the average values of the measured actual values of the baud rate (clock pulse interval) of the specified receiving slave node are read. For example, when the own node is the slave node SN1 and the receiving slave node is only the SN2, the transmission clock pulse interval set in the own node is calculated as follows. That is, in the actual value memory of FIG. 5, the average value of the clock pulse interval measurement values of the master node MN calculated and updated in S2 is f ¹ _mn , and the clock pulse of the reception slave node SN2 read out in S6 above Since the average value of the interval measurement values is stored as f ¹ _2n , these are read out, and the transmission clock pulse interval fp set in the own node is
fp = (f ¹ _mn + f ¹ _2n ) / 2
Calculate as On the other hand, when the receiving slave nodes are SN2 and SN3, the average values f ¹ _2n and f ¹ _2n of the clock pulse interval measurement values of the receiving slave nodes SN2 and SN3 are read and the transmission clock pulse interval fp set in the own node is read. The
fp = (f ¹ _mn + f ¹ _2n + f ¹ _3n ) / 3
Calculate as In both cases, the baud rate νp is
νp = 1 / fp
This value is output as a set frequency to the frequency dividing circuit 106 (FIG. 2), and the baud rate correction of the own node (transmission slave node) is performed.

  Next, when the own node is not designated as the transmission slave node in S4, the process skips S5 and S6 and proceeds to S7 to check whether or not the own node is designated as the reception slave node. If the own node is designated as the receiving slave node, the process proceeds to S8, the scheduling table is referred to identify the transmitting slave node, and the process proceeds to S9.

In S9, the actual value memory of FIG. 5 is referred to, and the average value of the measured actual values of the baud rate (clock pulse interval) of the specified transmission slave node is read. For example, when the local node is the slave node SN1 and the transmission slave node is SN5, the transmission clock pulse interval fp set in the local node is
fp = (f ¹ _mn + f ¹ _5n ) / 2
Calculate as The baud rate νp is
νp = 1 / fp
This value is output as a set frequency to the frequency dividing circuit 106 (FIG. 2), and the baud rate correction of the own node (receiving slave node) is performed.

  In S4 to S7, when the own node is not designated as either the transmission slave node or the reception slave node, S5, S6, S8, and S9 are skipped, and the baud rate correction is not performed. If no header is received in S1, the ID field is not received in S3, and the process jumps to S10. At this time, a response is received from the transmission slave node. That is, in S10, since it is possible to identify which node is the receiving slave node by the header (ID field) that has already been received (S8), the identification information of the receiving slave node is held in the memory.

  Subsequently, in S11, it is determined whether or not the slave synchronization field at the head of the response has been received. If it is received, the process proceeds to S12, and the specific information of the receiving slave node held in the memory is read. Then, the slave baud rate (clock pulse width) is measured by the above-described method from the slave time correction reference waveform in the slave synchronization field, and in S13, it is stored in the corresponding slave baud rate area of the actual value memory of FIG. Update the average value.

  In the above processing, in each slave node, when the own node is designated as the receiving slave node, the baud rate of the own node is corrected using only the actual baud rate measurement values of the master node and the transmitting slave node. . When the own node is designated as a transmission slave node, the baud rate of the own node is corrected using only the actual baud rate measurement values of the master node and the receiving slave node. In other words, by selecting only the baud rate measurement value of the slave node corresponding to the current communication partner and correcting the baud rate of the own node, the influence of the oscillation accuracy of the slave node not involved as the communication partner of the own node can be eliminated. It is possible to improve the correction accuracy.

  However, when the variation in oscillation accuracy between the slave nodes is relatively small, as shown in FIG. 6, in each slave node, the master node that is the communication partner and the actual value related to the baud rate measurement result of the slave node are Are stored without distinction (f1, f2, f3,...), And the baud rate measurement result values of all the nodes other than the own node (that is, slave nodes and master nodes other than the own node) are read out. For example, the set baud rate of the own node may be calculated as the average value.

  Therefore, in each slave node 10 (S), the baud rate correction means corresponds to the master node 10 (M) and the actual value related to the baud rate measurement result of the slave node 10 (S) with the information specifying the communication partner. Baud rate measurement result value storage means for storing in the attached form is provided, and the baud rate measurement result values stored in the baud rate measurement result value storage means are selectively read out corresponding to the current communication partner, and the baud rate measurement is performed. The baud rate of the slave node 10 (S) can be corrected based on the actual value. If only the baud rate measurement result value of the slave node 10 (S) corresponding to the current communication partner is selected and reflected in the baud rate correction of the own node, it is natural that the slave node is not involved as the communication partner of the own node. The influence of 10 (S) oscillation accuracy can be eliminated, and the correction accuracy can be increased.

  For example, in each slave node 10 (S), the baud rate correction means, when the slave node 10 (S) is designated as the receiving slave node 10 (S) by the master node 10 (M), the master at the time of reception. The latest measurement result of the baud rate and the latest measurement result of the slave baud rate related to the slave node 10 (S) on the transmission side are stored in the baud rate measurement result value storage means, and these master nodes 10 (M) In addition, the baud rate of the slave node 10 (S) can be corrected in consideration of each baud rate measurement result value related to the slave node 10 (S) on the transmission side. The baud rate measurement result value is updated using the latest measurement values of the master baud rate and slave baud rate. By adding past measurement results to the latest measurement values of the master baud rate and slave baud rate, it is possible to reduce the influence of measurement errors and variations, or environmental errors such as measurement temperature, and improve baud rate correction accuracy. When the slave node 10 (S) is designated as the receiving slave node 10 (S) by the master node 10 (M), the latest measured values of the master baud rate and slave baud rate are not taken into account, without considering the actual baud rate measurement values. It is also possible to correct the baud rate based only on the above. In this case, the baud rate measurement result value storage means can be omitted.

  On the other hand, in each slave node 10 (S), the baud rate correction means, when its own slave node 10 (S) is designated as the transmission slave node 10 (S), the master node 10 (M) and the slave node 10 (S ) Is read from the baud rate measurement result value storage means, and the baud rate of the slave node 10 (S) is corrected based on the baud rate measurement result value. You can also When the own node becomes the transmission slave node 10 (S), the node becomes the output source of the slave time correction reference waveform, so there is no room for using a new baud rate measurement result at the communication event for correction. However, if the past baud rate measurement result when the communication partner becomes the transmission node is stored as the actual value, the baud rate can be corrected even when the own node becomes the transmission slave node 10 (S) using this result. Thus, the correction accuracy can be improved.

  In each slave node 10 (S), the baud rate correction means stores the actual value related to the baud rate measurement result of the master node 10 (M) and the slave node 10 (S) as communication partners without distinguishing the communication partner. Measurement result value storage means is provided, the baud rate measurement result values of all nodes other than the own slave node 10 (S) stored in the baud rate measurement result value storage means are read, and the own slave node 10 is read based on the baud rate measurement result value. It can also be configured to correct the baud rate of (S). This method is not desirable when the difference in oscillation accuracy of the slave oscillation circuit 105RC is large, but when the specifications of the slave oscillation circuit 105RC are unified and the influence of lot variation is small and the oscillation accuracy is relatively uniform, A relatively good baud rate correction effect can be achieved, and the actual value related to the baud rate measurement result is adopted without distinguishing the communication partner, so that the correction method is simplified and the software development man-hours can be reduced.

Hereinafter, some examples showing the effects of the present invention will be described.
FIG. 11 shows an example of a baud rate error occurrence state between nodes when slave-slave communication is performed using slave node 1 as a transmission slave node and slave node 2 as a reception slave node. The baud rate error is indicated by a relative value based on the transmission slave node (that is, slave node 1), and the case where the baud rate is larger than that of the transmission slave node is represented by “+”, and the case where the baud rate is smaller is represented by “−”. . The relative error of the master node is relatively small as −0.4%, but the relative error of the slave node 2 is as large as −2.2%. When the slave node 1 receives a header from the master node, and when the slave node 1 returns a response to the master node, communication between the master and slave is performed, and the relative error is as small as −0.4%, and the above-described allowable range of ISO 9141 ( ± 1.0%: 2.0% in width). However, when the response of the slave node 1 is also received by the slave node 2, it is + 2.2% outside the allowable range.

Therefore, using both the slave time correction reference waveform and the master time correction reference waveform described above, the baud rate of the slave node 1 is corrected with the average value of the baud rates of the master node and the slave node 2 as a target. In the relative error conversion of the baud rate of the slave node 1, the average value of the value -0.4% for the master node and -2.2% for the slave node 2, that is,
{−0.4 + (− 2.2)} / 2 = −1.3%
Therefore, the relative error of the master node viewed from the slave node 1 is + 0.9%, and the relative error of the slave node 2 is −0. 9%, which can be all within the allowable range.

  Next, as shown in FIG. 13, in a network composed of a master node and five slave nodes, consider a case where slave node 3 is a transmission slave node and slave nodes 1 and 4 are reception nodes (slave node 3 is The relative error of the baud rate of each node as a reference is displayed in the figure). Then, when the baud rate correction of the slave node 3 is performed selectively using only the baud rate measurement value of the receiving node (hereinafter referred to as receiving node selection correction), the baud rate measurement values of all nodes including nodes not involved in communication are used. The effect is compared with the case of using (hereinafter referred to as all node correction).

In the case of the reception node selection correction, the baud rate of the slave node 3 is corrected with the average value of each baud rate of the master node, the slave node 1 and the slave node 4 as a target. The amount of correction is
{+0.4 (master) +2.2 (slave 1) +0.6 (slave 4)} / 3 = + 1.0% (the second decimal place is truncated)
Thus, the baud rate is corrected to be increased by 1.0%. On the other hand, in the case of all node correction,
{+0.4 (master) +2.2 (slave 1) +0.6 (slave 2) +0.6 (slave 4) +0.4 (slave 5)} / 5 = + 0.8% (the second decimal place is rounded down) display)
Thus, the baud rate is corrected by 0.8%. However, this correction amount is clearly smaller than in the case of receiving node selection correction.

  The result after correction is shown in FIG. Comparing with the correction effect in slave node 1 having the largest relative error with respect to slave node 3 (transmission), the relative error that was + 2.2% before correction is reduced by 1.0% in the reception node selection correction, and +1 .2%, with all node corrections reduced by 0.8% to + 1.4%. In either case, the error is reduced, but it can be seen that the effect of receiving node selection correction is greater. For ease of understanding, only the slave node 3 is shown as a result of the baud rate correction. Therefore, the corrected relative error is out of the allowable range for the slave node 1, but the slave node 1 also By performing baud rate correction, the relative error can be kept within an allowable range.

  Next, in the same system configuration shown in FIG. 15, a case where baud rate correction only between the master and slave is performed using only the master time correction reference waveform as in the conventional case, and the slave time correction reference waveform is also shown. A case where the baud rate correction between the slaves and the slaves is also performed will be described as an example, and the difference in the effects will be compared. Here again, the slave node 3 is a transmission slave node, and the reception slave node is only the slave node 1. The slave node 3 corrects the baud rate and synchronizes with the master node, but it is considered that there is ± 0.1% synchronization error at this time.

  First, as a comparative example, the slave node 3 is synchronized with the master node, thereby correcting the relative error with the master node, specifically, + 0.2% baud rate, as shown in FIG. . Then, the relative error with the slave node 1 which was + 2.2% before the correction is reduced by + 0.2%, and after the correction is + 2.0%, which is within the allowable range. However, this is a case where the synchronization error with respect to the master node is not taken into consideration, and when the synchronization error actually exists on the negative side, there is a concern that the corrected relative error is also outside the allowable range.

Therefore, as in the embodiment, considering the synchronization between the slave node 3 and the slave node 1, the baud rate of the slave node 3 is
{+0.2 (master) +2.2 (slave 3)} / 2 = + 1.2%
Therefore, as shown in FIG. 17, the relative error of the master node viewed from the slave node 3 is −1.0%, and the relative error of the slave node 1 is + 1.0%. Even if there is a synchronization error of ± 0.1%, it can be seen that it can be within an allowable range with a margin.

The block diagram which shows the example of whole structure of the serial communication network system of this invention. The block diagram of each node which comprises the communication network of FIG. The schematic diagram which shows the message frame structure of LIN communication which employ | adopted this invention as contrasted with the conventional structure. The schematic diagram of a scheduling table. The figure which shows the 1st example of the performance value memory in a slave node. The figure which shows a 2nd example similarly. Explanatory drawing which shows the outline of the communication procedure in the network of FIG. The flowchart which shows an example of the baud rate correction | amendment process according to this invention. The schematic diagram of the reference waveform for time correction. Explanatory drawing of baud rate measurement by a timer counter. The figure which shows an example of the baud rate error occurrence condition between nodes. FIG. 12 is an effect explanatory diagram when the present invention is applied to FIG. 11. The figure which shows the 1st system configuration used for the effect verification of this invention with a baud rate error. Explanatory drawing which shows the effect of this invention in the system of FIG. 13 by contrast with the case where receiving node selection correction | amendment is performed, and the case where all node correction | amendment is performed. The figure which shows the 2nd system configuration | structure used for the effect verification of this invention with the baud rate error. FIG. 14 is an operation explanatory diagram of a comparative example in which only master / slave synchronization is considered in the system of FIG. 13. FIG. 6 is a diagram for explaining the operation and effect of the embodiment in consideration of slave / slave synchronization.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Serial communication network system 10 (M) Master node 10 (S) Slave node 20 Serial communication bus 101 Microcomputer (baud rate correction means)
105Q (105C) Master oscillation circuit 105RC Slave oscillation circuit 106 Divider circuit (master transmission clock signal generation circuit, slave transmission clock signal generation circuit)
109 Timer counter (master baud rate measuring means, slave baud rate measuring means)
HD header BF break field SF (MS) master synchronization field IDF slave node specific field RSP response SF (SS) slave synchronization field DF data field CSF error check field

Claims (9)

A serial communication network system comprising one master node and a plurality of slave nodes connected by asynchronous serial communication,
A master time correction reference waveform transmitting means provided in the master node for transmitting a master time correction reference waveform reflecting the baud rate of the master node to the serial communication bus when performing communication between the slave node and the master / slave. When,
A slave that is provided in each of the slave nodes and that transmits a slave time correction reference waveform reflecting the baud rate of the slave node to the serial communication bus when performing communication between the slave and the slave that is a communication partner. Time correction reference waveform sending means;
A baud rate that is provided in each slave node and corrects the baud rate of the slave node based on both the master time correction reference waveform acquired from the master node and the slave time correction reference waveform acquired from another slave node. Correction means;
A serial communication network system comprising: The master node is provided with a master oscillation circuit that generates a master reference clock signal, and a master transmission clock signal generation circuit that downconverts the master reference clock signal to generate the master transmission clock signal,
Each of the slave nodes includes a slave oscillation circuit that generates a slave reference clock signal having a frequency corresponding to the master reference clock signal, and downconverting the slave reference clock signal to a frequency corresponding to the master transmission clock signal. A slave transmission clock signal generation circuit for generating a slave transmission clock signal, wherein the baud rate correction means measures the baud rate of the master node indicated by the master time correction reference waveform using the slave reference clock signal. Baud rate measuring means, and slave baud rate measuring means for measuring the baud rate of the slave node that is the communication partner indicated by the reference waveform for slave time correction using the slave reference clock signal, and the baud rate of the slave node is Master no Serial communication network system according to claim 1, wherein the measurement result of the baud rate, is corrected with reference to both the measurement result of the baud rate of the slave node serving as the communication partner.   The master baud rate measuring means and the slave baud rate measuring means measure clock pulse widths of the master time correction reference waveform and the slave time correction reference waveform, respectively, and the baud rate correction means includes the master time correction. 3. The serial communication network system according to claim 2, wherein the baud rate of the slave node is corrected based on an average value of a clock pulse width of the reference waveform for use and a clock pulse width of the reference waveform for correction of the slave time.   4. The serial communication network system according to claim 2, wherein the serial communication bus is a LIN communication bus. When transmitting data from the transmission slave node to the reception slave node, one of the plurality of slave nodes as a transmission slave node and the other one or more as a reception slave node,
The master node has a header in which a break field indicating the start of a message, a master synchronization field incorporating the master time correction reference waveform, and a slave node specification field for specifying the data transmission slave node are arranged in the communication bus A header sending means for sending to
Each of the slave nodes includes a header receiving means for receiving the header, and a slave incorporating the slave time correction reference waveform when the own slave node is designated as the transmission slave node indicated by the slave node specifying field. 5. The serial communication network system according to claim 4, further comprising response sending means for sending a response in which a synchronization field, a data field incorporating data to be transmitted, and an error check field are arranged to the communication bus.   In each of the slave nodes, the baud rate correction means stores a performance value related to a baud rate measurement result of the master node and the slave node that are communication partners in association with information for specifying the communication partner. A baud rate measurement result value stored in the baud rate measurement result value storage unit is selectively read out from the baud rate measurement result value corresponding to the current communication partner, and based on the baud rate measurement result value 6. The serial communication network system according to claim 2, wherein the baud rate of the slave node is corrected.   In each of the slave nodes, the baud rate correction means includes a master node and a transmission side stored in the baud rate measurement result value storage means when the slave node is designated as a reception slave node by the master node. The serial communication network system according to claim 6, wherein the baud rate of the slave node is corrected based on each baud rate measurement result value related to the slave node.   In each of the slave nodes, the baud rate correction means, when the slave node is designated as a transmission slave node, the baud rate measurement actual values for all the nodes that are transmission partners of the master node and the slave node. The serial communication network system according to claim 6, wherein the serial communication network system reads out from the baud rate measurement result value storage means and corrects the baud rate of the slave node based on the baud rate measurement result value.   In each of the slave nodes, the baud rate correction unit includes a baud rate measurement result value storage unit that stores a record value related to a baud rate measurement result of the master node and the slave node that are communication partners without distinguishing the communication partner. The baud rate measurement result values of all nodes other than the own slave node stored in the baud rate measurement result value storage means are read, and the baud rate of the own slave node is corrected based on the baud rate measurement result value. The serial communication network system according to any one of claims 2 to 5.

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