JP2912259B2 - Data transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission system for transmitting data in packets in response to polling.

[0002]

2. Description of the Related Art A data transmission system in which a master device and a plurality of slave devices are connected via a common transmission path and the slave device transmits data in packets by polling from the master device is well known. As shown in JP-A-2-16836, "Polling Data Communication System" and the like, generation of a packet in a conventional slave device of this type of data transmission system is performed irrespective of a polling cycle from a master device. The slave device generates a packet when the amount of data input to the device has reached a certain amount or when a certain time has elapsed since the previous packet generation.

However, if the polling cycle of the main unit is not constant and the input period of data to the slave unit (that is, the accumulation period of data to be transmitted) is not constant,
There is a problem that polling is wasted and data transmission is delayed.

FIG. 4 is a diagram for explaining such a problem. When the amount of data stored in a slave device reaches a certain amount (in FIG. 4, the maximum amount that can be stored in a packet), Is generated, for example, at timing t1 in FIG. 4, no packet is generated because the data amount has not yet reached a constant amount. Therefore, even if a polling signal arrives, the packet cannot be transmitted. At this point, there is no polling signal, and the packet is transmitted by the polling signal at timing t3.

That is, even though a considerable amount of data has already been accumulated at the timing t1, the timing of the arrival of the polling signal is not known, so that packet generation and
No transmission is performed, and these stored data are transmitted at timing t3, which causes a delay in data transmission. Also, a configuration in which a new packet is generated when a certain time has elapsed from the previous packet generation has the same problem as the problem shown in FIG.

[0006]

As described above, in the conventional data transmission system of the polling type, the polling cycle of the main unit is not constant, and the data input period to the slave unit (that is, accumulation of data to be transmitted). If the period is not constant, there is a problem that polling is wasted or data transmission is delayed.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and minimizes the data transmission delay even when the polling cycle of the main unit is not constant and the data input period to the slave unit is not constant. It is an object of the present invention to provide a data transmission method capable of limiting the use of unnecessary polling.

[0008]

According to the data transmission method of the present invention, a master unit and a plurality of slave units are connected via a common transmission line, and data is transmitted from the slave unit in packets by polling from the master unit. Data transmission method,
A means for adding time information until the next polling to the slave device to a polling signal transmitted from the master device to the slave device. The slave device receives the time information and sets a packet to enable transmission of a packet at this time. Means for determining a timing to start generation.

Also, a main unit for transmitting the polling signal to be transmitted to the slave unit by adding time information until the next polling to the slave unit, and receiving the time information and transmitting the packet at this time. Calculating timing to start packet generation and setting this timing in a timer, data storage for temporarily storing input data, and storing in the data storage in response to a timeout signal from the timer And a slave device having a packet generation unit for reading the generated data and generating a packet.

The data transmission method of the present invention has the above-described configuration, so that even in a data transmission in which the polling cycle of the main unit is not constant and the data input period to the slave unit is not constant, the slave unit can be used. By the time the next polling signal is received, it is possible to generate a packet storing the maximum amount of data.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the device configuration of the data transmission system of the present invention, FIG. 2 is a timing chart for explaining the operation of the present invention, and FIG. 3 is a flowchart for explaining the same operation. In the figure, 1
Is a main device, 2 is a slave device, and 3 is a common transmission line. In addition,
Although a plurality of slave devices are connected to the common transmission line 3, they are omitted in FIG. Further, the common transmission line 3 is not limited to the wired transmission line shown in FIG. 1, but may be a wireless transmission line. The slave device 2 includes an arithmetic unit 4 that calculates the timing of generating a packet, a timer 5 that outputs the timing of generating a packet, a packet generation unit 6 that actually generates a packet based on a signal from the timer 5, and a slave device 2. And a data storage section 7 for temporarily storing data input to the storage section.

Next, the operation will be described. In the data transmission method according to the present embodiment, as shown in FIG. 1, a main device 1 and a plurality of slave devices 2 are connected by a common transmission path 3, and a slave device 2 transmits a packet to the The polling signal includes time information (shown at T1 in FIGS. 2 and 3) until the next polling of the slave device 2. The slave device 2 that has received the polling signal transmits the already generated packet, receives the above-described time information T1, and subtracts the time T2 necessary for generating the packet from the T1 in the arithmetic unit 4 to calculate the time. T3 is calculated, and the time T3 is set in the timer 5.

When the time T3 has elapsed and the timer 5 has timed out, the packet generator 6 reads out the data stored in the data memory 7 during the time T3 and generates a packet. Therefore, when the next polling signal is received from the main device 1 after the time T1, the slave device 2 can immediately transmit the packet storing the data read out during the time T3 without delay. .

[0014]

As described above, according to the data transmission method of the present invention, a means for adding time information until the next polling to the slave device to the polling signal transmitted from the master device to the slave device, Means for receiving the time information and deciding the timing to start packet generation so as to enable transmission of the packet at this time, so that the polling cycle of the master device is not constant and the data to the slave device is not Even in data transmission where the input cycle is not constant, packets can be transmitted efficiently in response to the polling signal, thereby eliminating a data transmission delay. Also, packets can be sent out as long as there is data, and there is an effect that unnecessary polling is not performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an apparatus configuration of a data transmission system according to the present invention.

FIG. 2 is a timing chart for explaining the operation of the present invention.

FIG. 3 is a flowchart for explaining the operation.

FIG. 4 is a timing chart for explaining the operation of the conventional data transmission method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main apparatus 2 Slave apparatus 3 Common transmission line 4 Operation part 5 Timer 6 Packet generation part 7 Data storage part

Claims (2)

(57) [Claims] 1. A data transmission system in which a master device and a plurality of slave devices are connected via a common transmission path, and data is transmitted from the slave device in packets by polling from the master device. Means for adding time information until the next polling to the slave device to the polling signal to be transmitted. The slave device receives this time information and determines the timing to start packet generation so as to enable packet transmission at this time. A data transmission method, comprising: 2. A main unit for transmitting a polling signal to be transmitted to a slave device by adding time information until the next polling to the slave device, and receiving the time information and transmitting a packet at this time. Calculating timing to start packet generation and setting this timing in a timer, data storage for temporarily storing input data, and storing in the data storage in response to a timeout signal from the timer 2. The data transmission system according to claim 1, further comprising a slave device having a packet generation unit that reads out the generated data and generates a packet.