JP2692255B2 - Multi-drop communication method - Google Patents

Description

The present invention relates to an asynchronous multi-drop data communication system.

[Conventional technology]

In multi-drop communication in which a master station and a plurality of slave stations are connected as shown in FIG. 3, when the master station communicates with a specific slave station, first, a character sequence including the slave station number is transmitted, and the master station and the master station are connected. After establishing a data link with a slave station, data transmission / reception is executed.

At this time, the slave station returns the response sequence, but the other slave stations recognize that they are not addressed to themselves and discard the received character sequence.

After that, character transmission / reception between the master station and the slave station is executed, but other slave stations continue to discard all the received data.

[Problems to be solved by the invention]

In the conventional method described above, other slave stations that do not actually need to send and receive data also receive and discard the unnecessary character sequences, and the slave station MPU (microprocessor) continuously executes the processing for that purpose. Had to do.

Therefore, when the slave MPU executes other processing in parallel, there is a drawback that the processing capacity of the slave station decreases and the performance of the system deteriorates. In some cases, a communication dedicated MPU is required.

[Means for solving the problem]

The present invention has been made to solve the above-mentioned drawbacks, in which a master station is provided with a character sequence and break character transmission means, and a slave station is prohibited from receiving character sequence and break character and character sequence reception. Means, the slave station can receive the character sequence only after receiving the break character, and if it is not addressed to itself, the subsequent character sequence reception is prohibited, during data communication between the master station and the slave station, It is designed so that characters not addressed to itself are not received.

[Action]

In the communication of the multi-drop method by the above means,
It is not necessary for the MPUs of other slave stations that are not related to data transmission / reception to execute unnecessary character processing, and it is possible to prevent a reduction in the processing capacity of other parallel processing that the MPU should execute.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

 FIG. 1 is a block diagram inside each slave station.

The character sequence and the break character from the main station pass through the communication line 1 and the receiver of the transceiver 2
It is sent to UART3 (communication control device) through 21. When the received character is a break character, it is detected by the break character detection unit 32, and the break interrupt signal 52 is generated to the MPU 5. Upon receiving the break interrupt, the MPU 5 inverts the reception interrupt disable signal 53 to the enable level.
After the break character, the character sequence including the slave station number transmitted from the master station is received by the character receiver 31 of the UART3, the reception completion signal 55 passes through the AND circuit 4, and the reception interrupt signal 51 is notified to the MPU5. It The slave station confirms whether or not the received character sequence is addressed to itself, and if it is addressed to itself, outputs a transmission permission signal 54 to put the transmitter 22 into the operation mode, and the UART3
The response character sequence is transmitted from the transmission unit 33 of.

On the other hand, when the received character sequence is not addressed to itself, the MPU inverts the reception interrupt prohibition signal 53 to the prohibition level and prohibits the reception of the subsequent character sequence.

FIG. 2 is a flowchart showing the internal processing of the master station and each slave station when the above sequence is executed.

First, the master station transmits a break character (201), then transmits a character sequence including the slave station number of the other party with whom the data link is desired to be established (202), and then enters a reception waiting state (203).

When the response from the slave station is received (204) and the data link is established, the communication with the slave station is executed (20).
Five).

On the other hand, in the slave station, after receiving the break character (206), the reception interrupt is enabled (207).

After that, the character sequence from the main station is received (208) and its contents are checked (209).

When the slave station number designated by the master station is not addressed to itself, the subsequent reception interrupt is prohibited (213), and the processing is terminated.

If it is addressed to itself, the necessary response character sequence is transmitted to the main station (210), and then the reception interrupt is enabled (211).

After that, the data communication is executed according to the command from the master station (212).

〔The invention's effect〕

As described above, according to the present invention, in multi-drop communication, other slave stations irrelevant to data transmission / reception
The MPU only needs to execute the character processing when the data link is established when a break interrupt occurs, and it is not necessary to execute other unnecessary character processing, preventing a decrease in the processing capacity of other parallel processing that the MPU should execute. This has the effect that the performance of parallel processing can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of the inside of each slave station in an embodiment of the present invention, FIG. 2 is a flowchart showing the internal processing of the master station and slave stations, and FIG. 3 is a diagram showing the configuration of a general multi-drop communication system. Is.

Claims (1)

(57) [Claims] 1. A means for transmitting a character sequence, which is a plurality of characters arranged in time series, and a normal data having a special bit pattern when establishing a data link prior to the transmission of the character sequence. A master station having means for transmitting a break character and a plurality of slave stations having means for receiving a character sequence including the break character, and communication is performed between one master station and a plurality of slave stations. In an asynchronous multi-drop communication device, each slave station outputs the MPU, a character receiver, a break character detector that generates a break interrupt signal to the MPU when a break character is detected, and the output of the character receiver. A gate circuit capable of selecting whether to output to the MPU, When the break interrupt signal is input, the MPU inverts the reception interrupt disable signal to the gate circuit to the enable level, and when the reception of the break character is detected, the character sequence for the own station following the break character is received. In this case, the multi-drop communication device is characterized in that it accepts a subsequent character sequence and prohibits the subsequent character sequence from being accepted when a character sequence not addressed to itself is received.