JPH0629962A - Method and equipment for multiplex transmission - Google Patents

Abstract

PURPOSE:To attain flexible arbitration taking the priority into account even when a transmission request comes with a delay more or less. CONSTITUTION:Units 1, 2 are connected to one and same common bus. The transmission processing from each of the units 1, 2 is implemented by sending data SOF indicating start of transmission, data PRI indicating priority, substantial data DATA to be sent and data EOF indicating end of transmission in this order to the common bus. When the unit 1 starts transmission of the SOF already at a time t2 when the unit 2 makes a transmission request, the unit 2 sends the PRI2 in matching with the end timing of the SOF. The unit 1 sends the PRI1 simultaneously and then collision takes place. When the priority of the PRI2 is higher than that of the PRI1, the PRI2 is valid on the common bus and the unit 1 stops its transmission. The unit 2 acquiring the transmission right on the way of transmission of the unit 1 finishes its transmission up to a time t4. The unit 1 starts the transmission again from the time t4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for multiplex transmission, and more particularly, multiple units can be connected to the same common bus and time-divisionally used for the common bus to enable multiplex transmission between plural units. The present invention relates to a multiplex transmission method and device.

[0002]

2. Description of the Related Art A system for performing multiplex transmission between a plurality of units by connecting a plurality of units to the same common bus and using this common bus in a time division
It is used in various fields. An important issue in such a multiplex transmission system is to properly arbitrate signal collisions on the common bus. As a general rule, only one unit can transmit data to the common bus at the same time, and when a plurality of units make transmission requests at the same time, it is necessary to properly arbitrate this.

Usually, a plurality of units connected to a common bus have different degrees of importance. For this reason, it is general that the priority is defined for each data to be transmitted and the arbitration is performed in consideration of this priority. For example,
Japanese Unexamined Patent Publication No. 2-116235 discloses a technique of constantly monitoring the state of the common bus and performing priority determination at the time of signal collision without delay. Japanese Unexamined Patent Publication No. 1-143537 discloses the trial time and the number of trials. A technique for increasing the priority in accordance with the above is disclosed.

[0004]

In the conventional arbitration method considering priority, when a plurality of units simultaneously issue a transmission request, the transmission from the unit with a high priority is always permitted. However, if the transmission request from one unit lags behind the transmission request from the other unit, the unit that made the transmission request as soon as possible regardless of the priority You will acquire the transmission right. For this reason, a unit with a slightly delayed transmission request may acquire the transmission right until the transmission process of the unit that started transmission earlier is completed, even if the priority is very high. I can not do it.

Therefore, an object of the present invention is to provide a multiplex transmission method and apparatus capable of performing flexible arbitration in consideration of priority even when a transmission request is delayed a little.

[0006]

[Means for Solving the Problems] (1) In the first invention of the present application, a plurality of units are connected to the same common bus, and the common bus is used in a time division manner to perform multiplex transmission between the plurality of units. In the multiplex transmission method that enables the transmission processing from each unit, each data of the data SOF indicating the start of transmission, the data PRI indicating the priority, the original data DATA to be transmitted, and the data EOF indicating the end of transmission are When the data SOF from another unit has already been transmitted to the common bus when the transmission processing from one target unit is performed, the data SOF of this other unit is transmitted.
The data PRI is sent from the unit of interest in accordance with the end timing of the, and a collision occurs on the common bus with the data PRI sent from another unit. As a result of the collision, the data PRI of the unit of interest is sent. If the higher priority is shown, the data unit DATA and the data unit EOF are continuously transmitted from the target unit, the data transmission from another unit is stopped, and as a result of the collision,
When the data PRI sent by another unit has a higher priority, the data DATA and the data EOF are subsequently sent from another unit, and the data sending from the unit of interest is stopped. Is.

(2) A second invention of the present application is a multiplex transmission system which enables multiplex transmission between a plurality of units by connecting a plurality of units to the same common bus and using the common bus in a time division manner. In the multiplex transmission device used in each unit, the data SOF indicating the start of transmission, the data PRI indicating the priority,
A transmission buffer holding the original data DATA to be transmitted and data EOF indicating the end of transmission, data transmission means for transmitting the data in this transmission buffer to the common bus in a predetermined order, and this data transmission means are operated. For controlling the supply of the transmission clock to the data transmission means while monitoring the common bus and the transmission clock generation means for generating the transmission clock for transmission, and instructing the transmission order of the data in the transmission buffer and performing the transmission processing A control means is provided, and when the control means performs transmission processing, when the common bus is in an empty state, control is performed such that the data in the transmission buffer is sent in the order of SOF, PRI, DATA, and EOF. When the control means performs the transmission process, the data SOF from another unit has already been sent to the common bus. At times, the data PRI in the transmission buffer is transmitted in synchronization with the end timing of the data SOF of the different unit, causing a collision on the common bus with the data PRI transmitted from the different unit. As a result, when the data PRI sent by itself has a higher priority, the data DATA and the data EOF in the send buffer are continuously sent, and as a result of the collision, the data PRI sent by another unit is changed. In the case where the higher priority is shown, the control for canceling the transmission processing is performed until the transmission from another unit is completed.

[0008]

[Operation] In the transmission process in the multiplex transmission method using the common bus, each data of the data SOF indicating the start of transmission, the data PRI indicating the priority, the original data DATA to be transmitted, and the data EOF indicating the end of transmission are It is generally performed by sequentially sending out to a common bus. In the conventional arbitration method, even if the preceding unit has already begun to send out the data SOF on the common bus, it is no longer able to deprive the preceding unit of the transmission right. , Had to wait until the transmission process of this preceding unit was completed. On the other hand, in the present invention, when the preceding unit has already transmitted the data SOF to the common bus, the data PRI is transmitted at the end timing of the data SOF of the preceding unit. Therefore, data P from multiple units
RI will collide on the common bus. By using a so-called collision detect method, when such a collision occurs, only the data PRI having a higher priority can be made effective on the common bus. According to the present invention, each unit determines the difference in priority at the time of collision of the data PRI, and the data DATA and the data EOF subsequent to the data PRI are sent only to the unit having a high priority. For this reason, even if a unit with a low priority has already started sending the data SOF, a unit with a high priority can take away the transmission right from the middle.

[0009]

The present invention will be described below based on illustrated embodiments. FIG. 1 is a diagram showing an outline of a general multiplex transmission system using a common bus. In this example, five units 1 to 5 are connected to the common bus 100.
Since it is not possible to transmit a plurality of data to the common bus 100 at the same time, the transmission right is given to only one unit at the same time point, and so-called time division multiplex transmission is performed.

FIG. 2 shows an example of a data format generally used in such a time division multiplex transmission system. In general, the transmission process from each unit includes data SOF (abbreviation of Start Of Frame) indicating transmission start, data PRI (abbreviation of PRIority) indicating priority, original data DATA to be transmitted, data EOF indicating transmission end. (End Of Fr
ame), and each data is sent to the common bus in this order. FIG. 2A shows this general data format. Where SOF and E
OF is a predetermined code common to all units, but PR
For I, a different code is set for each unit. Also, DATA naturally has a different value for each unit. Therefore, for example, the data transmitted by the unit 1 is SOF, PRI1, DA as shown in FIG. 2 (b).
Although it becomes TA1, EOF, the data sent by the unit 2 is SOF, PRI2, DAT as shown in FIG. 2 (c).
It becomes A2, EOF.

Now, if transmission requests are issued from the units 1 and 2 at the same time, SOFs are simultaneously sent from both units to the common bus 100, and subsequently PRI1 and PRI2 collide with each other on the common bus. . When codes with such a priority collide on the common bus, it is usually the Collision Detec.
By the method of t), the code with the higher priority becomes effective on the common bus. For example, on the common bus,
If the hardware configuration is such that the logic "1" becomes valid when the logic "0" and the logic "1" collide (conversely, the logic "0" may become valid). ,
The higher the number, the higher the priority. Let me explain this with a concrete example. If the PRI is a 4-bit code, PRI1 = “0011” and PRI2 = “010”.
Suppose it was 1 ”. Assuming that one bit at a time is sent to the common bus 100 from the upper bit side of these codes, first, the logic "0" of PRI1 and PRI2.
And a logic "0" are transmitted on the common bus. Since the same logical value happens to be the same, the common bus becomes a logical "0" and the problem of collision does not occur. However, the second bit is PRI1
Logic "0" of PRI2 and logic "1" of PRI2 are transmitted to the common bus, and a logic collision occurs. In this case, if the hardware is configured such that the logic "1" is valid, the common bus becomes the logic "1". At this point, the unit 1 can recognize that the common bus is actually at the logic "1" even though the unit 1 sends out the logic "0". In this way, when the logic it is sending cannot be correctly sent to the common bus, it is determined that a collision with another unit having a higher priority has occurred, and transmission processing thereafter is stopped. Therefore, for the third and fourth bits, only PRI2 is transmitted, and thereafter, only DATA2 is transmitted. This is a commonly used collision detect method.

In the conventional multiplex transmission method, as described above,
When a plurality of units simultaneously issue transmission requests and simultaneously start sending SOF, a unit with a higher priority acquires the transmission right and a unit with a lower priority stops the transmission. However, if the transmission request is delayed even slightly, the transmission right is always given to the unit that has started the transmission of the SOF first. This will be shown in the time chart of FIG. Now, consider a case where the unit 1 issues a transmission request at time t1 and the unit 2 issues a transmission request at a time t2 which is slightly delayed from this. At time t1, if the common bus is idle, unit 1 acquires the transmission right and starts sending SOF to the common bus. Therefore, at time t2, even if the unit 2 issues a transmission request, the unit 2 cannot obtain the transmission right because the SOF from the unit 1 has already been sent to the common bus. The unit 1 continues the transmission process as it is, and by the time t1 to t3, SOF, PRI
1, DATA1, EOF are transmitted. At time t3, the unit 2 recognizes that the transmission of the EOF is completed on the common bus, and secures the transmission right for the first time here. In this way, the unit 2 is set to S by the time t3 to t4.
It sends OF, PRI2, DATA2, and EOF. Eventually, the data as shown in the figure will be transmitted to the common bus. Such a transmission procedure is independent of priority. That is, even if PRI2 has a higher priority than PRI1, if unit 1 starts transmitting earlier, unit 2 will have to wait for the completion of transmission of unit 1. This is a problem of the conventional multiplex transmission method.

The multiplex transmission method of the present invention solves such a problem by performing the following processing. Now, consider a case where the unit 1 issues a transmission request at time t1 in the time chart of FIG. 4 and the unit 2 issues a transmission request at time t2 which is a little later than this. At time t1, if the common bus is empty, the unit 1 acquires the transmission right for the time being, and the SOF
To send to the common bus. Next, at time t2, the unit 2 issues a transmission request. According to the present invention, each unit monitors the common bus when performing the transmission process, and if the SOF from another unit has already been transmitted, the PRI is transmitted at the end timing of the SOF of the other unit. I do. That is, in the example shown in FIG. 4, the SOF from another unit 1 has already been sent to the common bus at the time t2 when the unit 2 tries to transmit. Therefore, the unit 2 sends out PRI2 at the time t3 which is the end timing of this SOF (the unit 2 does not send out SOF). On the other hand, the unit 1 which has started the transmission first tries to transmit the PRI1 subsequent to the SOF. Therefore, the PRI1 and PRI2 collide on the common bus.

This collision is handled by the above-mentioned collision detect method. For example, PRI1 =
If “0011” and PRI2 = “0101”,
Consider a case where the priority of PRI2 is higher. in this case,
As described above, at the time when the second bit is transmitted to the common bus, the unit 1 recognizes that a collision with a unit having a high priority has occurred, and abandons the transmission right that has been acquired so far. That is, the unit 1 stops the transmission process when the PRI 1 has been transmitted halfway. On the other hand, the unit 2 recognizes that the transmission right has been taken due to the normal transmission of the PRI 1 to the common bus.
Send out ATA2 and EOF. Eventually, on the common bus, SOF and PRI are reached by the time t1 to t4.
2, DATA2, EOF will be transmitted. Here, the SOF is actually sent by the unit 1, and the subsequent PRI2, DATA2, and EOF are the unit 2
Was sent by. However, the side receiving these data can receive them in the correct data format of SOF, PRI2, DATA2, EOF, so that it can be handled in the same way as when the unit 2 sends all the data. In this way, when the unit 2 completes the transmission at the time t4, the unit 1 restarts its own data transmission process from the beginning, until the time t4 to t5.
SOF, PRI1, DATA1, and EOF are transmitted.

By comparing the result of the conventional multiplex transmission method shown in FIG. 3 with the result of the multiplex transmission method of the present invention shown in FIG. 4, it is easy to understand that the conventional problems have been solved by the present invention. You can understand. That is, according to the present invention, even if the transmission request of the unit 2 having a high priority is slightly delayed from the transmission request of the unit 1 having a low priority, the transmission right of the unit 1 can be transmitted from the unit 2 by the unit 2 from the middle. Since it can be captured, arbitration that faithfully considers the priority becomes possible.

FIG. 5 is a block diagram showing an example of a multiplex transmission device for carrying out the multiplex transmission method as shown in FIG. If the multiplex transmission device as shown in FIG. 5 is provided in each unit, the multiplex transmission method according to the present invention becomes possible. In the block diagram of FIG. 5, the data to be transmitted is
It is temporarily stored in the transmission buffer 10. In the figure, SOF, PRI, DATA, and EOF are stored in the transmission buffer 10.
However, the state in which they are held in this order is shown. The data in the transmission buffer 10 is sequentially transferred to the shift register 20. The shift register 20 has a function of sending the transferred data bit by bit from the upper side to the common bus 100 as transmission data. This bit-by-bit shift operation is performed by supplying the transmission clock generated by the transmission clock generating means 30. On the other hand, such control of the transmission process is performed by the transmission control means 40. The transmission control means 40 is the common bus 10.
While monitoring 0, it outputs a control signal to be given to the AND gate 50 and instructs the order of data transmission to the transmission buffer 10. The AND gate 50 permits or prohibits the supply of the transmission clock generated by the transmission clock generation means 30 to the shift register 20 based on the control signal given from the transmission control means 40.

The transmission control means 40 has a function of constantly monitoring the common bus and performing a normal transmission process performed by a conventional multiplex transmission device and a transmission process peculiar to the present invention. Hereinafter, these processes will be specifically described. The normal transmission process is a process of transmitting when the common bus is idle. That is, when the predetermined data is prepared in the transmission buffer 10 and the actual transmission processing is performed,
If the common bus is empty, a control signal for permitting the supply of the transmission clock is given to the AND gate 50, and the SOF,
It gives an instruction to send in the order of PRI, DATA, and EOF. As a result, the shift register 20 has an SO
Data is transferred in the order of F, PRI, DATA, and EOF, and one bit of data is sent to the common bus 100 for each cycle of the transmission clock. During the transmission process, the transmission control means 40 keeps the common bus 10
0 is monitored to determine whether the transmitted bit is a valid bit on the common bus 100. If the transmitted bit and the bit actually appearing on the common bus 100 are different, it is determined that the bit collides with the transmission data from the unit having a higher priority, and the transmission process is stopped. That is, the AND gate 50 is given a control signal for prohibiting the supply of the transmission clock, and the transmission buffer 10 is given an instruction for returning the sending order. In this case, when the common bus becomes empty again, SOF, PRI, DATA, EO
The data transmission in the order of F is executed again.

On the other hand, the transmission process peculiar to the present invention is a process when it is detected that the data SOF from another unit has already been transmitted to the common bus 100 during the transmission process. At this time, for the time being, a control signal for prohibiting the supply of the transmission clock is given to the AND gate 50. Therefore, at this time point, data transmission to the common bus 100 is not performed. The transmission control means 40 continues to monitor the common bus 100, recognizes the end timing of the SOF sent by another unit, and supplies a control signal for permitting the supply of the transmission clock to the AND gate 50 in accordance with this end timing. The transmission buffer 10 is instructed to skip the SOF and set the transmission order to PRI, DATA, and EOF. As a result, the PRI is first transferred to the shift register 20, and one bit is sent to the common bus 100 from the upper side of the PRI. That is, a collision with the PRI sent by another unit on the common bus occurs. During this transmission process, the transmission control means 40 monitors the common bus 100 and determines whether the transmitted bit is a valid bit on the common bus 100. If the transmitted bit and the bit actually appearing on the common bus 100 are different, it is determined that the bit collides with the transmission data from the unit having a higher priority, and the transmission process is stopped. That is, a control signal for prohibiting the supply of the transmission clock is given to the AND gate 50, and
The transmission buffer 10 is instructed to restore the sending order. If the transmitted bit and the bit actually appearing on the common bus 100 match, it is determined that the transmission right can be taken from the middle, and DATA and EOF are continuously transmitted after PRI.

As described above, by using the device shown in FIG.
The multiplex transmission method shown in FIG. 4 can be implemented. Although the present invention has been described above based on the illustrated embodiments, the present invention is not limited to these embodiments,
Other than this, it can be implemented in various modes. In particular, the block diagram shown in FIG. 5 shows an example of a hardware configuration for implementing the present invention, and other various hardware can be used to implement an equivalent device. Further, the data format shown in FIG. 2 is an example, and in addition to this, an area indicating the type and length of data, an area for storing an error check code, and the like may be provided.

[0020]

As described above, according to the present invention, even if the preceding unit has already transmitted the data to the common bus, the transmission right can be intercepted by the unit having the higher priority. Therefore, even if the transmission request is delayed a little, it becomes possible to perform flexible arbitration in consideration of the priority.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a general multiplex transmission system using a common bus 100.

FIG. 2 is a diagram showing an example of a general data format used in the multiplex transmission system shown in FIG.

FIG. 3 is a time chart showing problems in the conventional multiplex transmission method.

FIG. 4 is a time chart showing that the problem shown in FIG. 3 has been solved by the multiplex transmission method of the present invention.

FIG. 5 is a block diagram showing a configuration of a multiplex transmission device according to an embodiment of the present invention.

[Explanation of symbols]

 1 to 5 ... Unit 10 ... Transmission buffer 20 ... Shift register 30 ... Transmission clock generation means 40 ... Transmission control means 50 ... AND gate 100 ... Common bus SOF ... Data indicating start of transmission PRI ... Data indicating priority DATA ... To be transmitted Original data EOF ... Data indicating the end of transmission

Claims (2)

[Claims] 1. A multiplex transmission method which enables multiplex transmission between a plurality of units by connecting a plurality of units to the same common bus and using the common bus in a time division manner. Data S that indicates the start of transmission
Each of the OF, the data PRI indicating the priority, the original data DATA to be transmitted, and the data EOF indicating the end of transmission is sent to the common bus in this order, and when the transmission processing from one unit of interest is performed. , When the data SOF from another unit has already been sent to the common bus, the data PRI is sent from the unit of interest in accordance with the end timing of the data SOF of this other unit, and sent from the other unit. Data PRI that causes a collision on the common bus, and as a result of the collision, the data P sent by the unit of interest.
If RI indicates a higher priority, subsequently, the data unit DATA and the data EOF are transmitted from the target unit, the data transmission from the another unit is stopped, and as a result of the collision, the other unit Data P sent by the unit
When RI indicates a higher priority, the data transmission and the data EOF are continuously transmitted from the different unit, and the data transmission from the unit of interest is stopped. 2. A plurality of units are connected to the same common bus, and each unit is applied for application to a multiplex transmission system that enables multiplex transmission between the plurality of units by time-divisionally utilizing the common bus. , Which is a multiplex transmission device used in, data SOF indicating start of transmission, data PR indicating priority
I, original data DATA to be transmitted, and data EOF indicating the end of transmission, a transmission buffer, data transmission means for transmitting the data in the transmission buffer to a common bus in a predetermined order, and the data transmission means. A transmission clock generating means for generating a transmission clock for operating and a common bus being monitored, while controlling the supply of the transmission clock to the data transmitting means and instructing a transmission order of the data in the transmission buffer. Transmission control means for performing transmission processing, and, when the control means performs transmission processing, when the common bus is in an empty state, the data in the transmission buffer is
When the data SOF from another unit has already been sent to the common bus when the control means performs the sending process in the order of sending SOF, PRI, DATA, and EOF, this another unit is sent. Data PRI in the transmission buffer is transmitted in accordance with the end timing of the data SOF of the data PR.
When a collision occurs on the common bus with I, and as a result of the collision, the data PRI transmitted by itself has a higher priority, the data DATA and the data EOF in the transmission buffer continue. And, as a result of the collision, the data PRI sent by the different unit has a higher priority, control for stopping the transmission process until the transmission from the different unit is completed. A multiplex transmission device characterized by performing.