JPH05145558A - Data transmission control system - Google Patents

Abstract

PURPOSE:To prevent a delay in a response from a center equipment from being caused by preventing a communication interruption from other terminal equipment to a terminal equipment during data transmission with respect to the data transmission control system in which plural terminal equipments connected with a multidrop line to a center equipment make data transmission to the center equipment in a contention form. CONSTITUTION:Each terminal equipment 1 is provided with a carrier detection section 18 detecting an idle communication line and outputting an off-signal and with a CD holding circuit 17 outputting a CD signal set for a prescribed time even after an output of the carrier detection section 18 is OFF. Moreover, a holding time of the CD latch circuit 17 is controlled to be reduced during data transmission from its own terminal equipment and the terminal equipment making data transmission detects earlier an idle communication line than the other terminal equipment to implement transmission of a succeeding data block with priority over the other terminal equipment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission control system when a plurality of terminals connected to a center device by a multi-drop line transmit data to the center device in a contention format.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a data transmission system such as a building management system to which the present invention is applied, and FIG. 5 is a transmission sequence in the prior art.

In a building management system or the like, as shown in FIG. 4, a plurality of terminals 1-1 to 1-3 are installed on each floor or each tenant in the building, and are connected via a multi-drop type communication line 3. It is connected to the center device 2. Residents on each floor set control data (air conditioning operation time, desired room temperature, etc.) for their own living environment to the center device 2 using the terminals 1-1 to 1-3, and the center device 2 uses this control data to control the building. Control equipment.

In order to set the above-mentioned data in the center device 2 and to receive information on the management status of the building (control information of the center, control schedule, etc.), the resident can use the terminals 1-1 to 1-3.
The data is transmitted to the center device 2 via.

This transmission sequence is as shown in FIG.
A series of transmission data is divided into a plurality of blocks, and the data blocks are sequentially transmitted to the center device 2. Since each terminal shares a communication line, the contention format is adopted in order to prevent simultaneous data transmission from a plurality of terminals. That is, each terminal monitors whether the line is idle by detecting the carrier on the line,
After confirming that the carrier detection CD is "0", that is, no data transmission is being performed between another terminal and the center apparatus, the transmission request ENQ is sent to the center apparatus.

For example, when a transmission request is issued to the terminal # 1, a transmission request ENQ is sent to the center device. Upon receiving the ENQ, the center device returns an acknowledgment ACK to the terminal # 1 when the preparation for data reception is completed. Upon receiving the ACK, the terminal # 1 confirms that there is no carrier on the line and then transmits the first transmission data block D # 1. When the center device receives this, it returns ACK, thereafter similarly sequentially transmits a predetermined number of data blocks, finally transmits a transmission completion notification EOT, and a series of data transmission ends.

[0007]

However, the center device receives the transmission request ENQ and the data block and then the AC
It takes a finite response time to send the next data block after the terminal receives ACK until K is returned. Further, a signal propagating on the line requires a propagation time. For this reason, there is a period during which no signal exists on the line during a period in which a certain terminal (terminal # 1) and the center apparatus exchange a series of data. If a transmission request happens to another terminal (terminal # 2) within this period, the carrier detection signal is off (“0”), so terminal # 2 misrecognizes that the line is idle and sends ENQ. Then, the center device returns a negative acknowledgment NACK (a response indicating that the request is not accepted because the terminal is in data communication with another terminal) to this terminal # 2. During this time, since the carrier detection of the terminal # 1 is turned on, the terminal # 1 has to wait for the transmission of the next data block, and the end of the data transmission is delayed, so that the quick response from the center device cannot be obtained. Occurs.

That is, in a system in which a series of information to be transmitted is divided into a plurality of blocks and transmitted to the center device,
When data is transmitted between a certain terminal and the center device, if a request for data transmission is made to another terminal device, an interrupt occurs and the communication end time of the terminal being transmitted is delayed. This is a drawback that the response of the center device is slow from the operator's point of view, and the serviceability of the system deteriorates.

The present invention has been made in view of these problems, and prevents a communication interrupt from another terminal with respect to a terminal that is transmitting data, so that a delay in response from the center device does not occur. The purpose is to

[0010]

FIG. 1 is a principle block diagram of a data transmission control system of the present invention. In order to solve the above problems, the data collection method of the present invention is as shown in FIG.
In a system including a center device 2 and a plurality of terminals 1 connected to the center device 2 by a multi-drop type communication line 3 and transmitting data to the center device 2 by a contention method, each terminal 1 , A carrier detection unit 18 that detects the vacancy of the communication line and outputs OFF, and a CD holding that outputs a CD signal that remains ON for a predetermined time even after the output of the carrier detection unit 18 becomes OFF Circuit 17 and the CD holding circuit during data transmission from its own terminal
By controlling so that the holding time of 17 is shortened, the terminal that is transmitting data can detect the vacancy of the communication line earlier than other terminals and send the next data block with priority over other terminals. Will be resolved.

[0011]

When the own terminal is not transmitting data, the carrier detection signal CD is kept on for a predetermined time even after the line becomes idle. By setting this holding time to be longer than the time (due to the propagation time or the response time) during which the data exchange between the other terminal and the center device during data transmission is interrupted, the own terminal is set to the other terminal and the center device. Carrier detection signal CD during the period when a series of data communication with
Are output continuously. Therefore, the transmission request is not issued during the transmission of the other terminal, and the communication interruption is prevented.

On the other hand, since the terminal which has started data transmission shortens the holding time of the CD holding circuit, when the carrier due to the ACK from the center device disappears, it immediately detects the vacancy of the line and the succeeding data block is detected. You can send. Therefore, during data transmission, the plurality of data blocks can be continuously transmitted to the center device without being interrupted by another terminal, and the response from the center device can be speeded up.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 2 shows an embodiment of the data transmission system of the present invention, and FIG. 3 shows the transmission sequence of the present invention. Note that the same reference numeral represents the same object throughout the drawings. Transmission device, FIG. 3 is a flowchart showing the operation.

FIG. 2A shows the structure of one terminal. 11 is a data transmitter / receiver, 12 is an AND gate, 13 is a line driver, 14 is a line receiver, 15 is an RS-CS timer, and 16 is a line receiver. A flip-flop, 17 is a CD holding circuit, and 18 is a carrier detection unit. The data transmission / reception unit 11 receives a transmission request signal when a data transmission request to the center device is generated by the operation of the operator or at a predetermined time.
RS "1" is output to open the AND gate 12, and "1" is input to the transmission enable signal CS obtained by delaying the RS signal by the RS-CS timer 15 for a predetermined time. Then, the transmission data SD is sent to the multi-drop line 3 via the line driver 13. The carrier detection unit 18 constantly monitors the reception signal received by the line receiver 14 from the line 3 except when the own terminal is transmitting, and outputs "1" when there is a signal on the line to detect the line Detects free status. CD holding circuit
When the output of the carrier detection unit 18 is input, and 17 is "1", the output 17 outputs "1", and the input "1" to "0".
After changing to, the output is "1" for a preset time.
This holding time can be set in two stages of t1 and t2 (t2 <t1) by the control signal from the flip-flop 16. That is, when the control signal is "1" after the line becomes idle and the carrier does not exist, during t2,
When it is "0", the carrier detection signal CD is held at "1" for a time t1 shorter than t2. Then, t1 is set to be longer than the no-carrier period based on the response time or signal propagation time of the terminal or center device that is transmitting and receiving a series of data, and t2 is sufficiently shorter than t1 and the carrier The guard time is set so short that the carrier detection signal does not become "0" due to disconnection or the like.

As shown in the operation time chart of FIG. 2 (b),
Normally, the carrier detection signal CD becomes "0" at t1 time after the reception data RD disappears. That is, the flip-flop 16 is reset at the previous fall of the carrier detection signal CD, and the control signal "0" is applied to the CD holding circuit 16.

When a data transmission request is issued from the own terminal, the data transmission request signal RS becomes "1".
16 is set and the Q output "1" is the CD holding circuit 17
, The CD holding time is set to a short t2 thereafter, and when the carrier disappears, the CD becomes "0" after t2. And
At the trailing edge of the carrier detection signal CD, the FF 16 is reset and the Q output of "0" causes the holding time of the CD holding circuit 17 to become t2, thereby returning to the normal waiting state.

That is, the CD holding time at the terminal after data transmission is shortened from t2 to t1. Next, the transmission sequence in the present invention will be described with reference to FIG. It is assumed that when no terminal is transmitting data and the line is in an idle state, a transmission request for data including two data blocks D # 1 and D # 2 is issued to the terminal # 1. When the terminal # 1 sends a transmission request ENQ to the center apparatus and receives an ACK signal from the center apparatus after the signal propagation time and the center apparatus response time, it transmits the first data block D # 1 and sends an ACK.
When the second data block D # 2 is received, a series of data is transmitted to the center device by transmitting the second data block D # 2 and finally the EOT indicating the end of the data transmission.

At this time, the line state becomes as follows, and a carrier nonexistence period occurs during data transmission / reception. The carrier detection signal of each terminal connected to this line by multi-drop is ,. That is, in the terminal # 1 which has started the data transmission, the CD holding time is set to a short t1, so that the CD detection becomes “0” immediately after receiving the ACK from the center apparatus, and therefore the transmission of the next data block is performed. Can be done subsequently. In terminal # 2, the holding time of the CD holding circuit is set to t1, which is longer than the carrier disconnection time. Therefore, until the series of data transmission / reception between terminal # 1 and the center device is completed, the carrier detection signal is "1". The transmission request ENQ is not transmitted even if a transmission request is generated during that period. And the last A after the call on the terminal 1 ends
After t2 from the time when CK disappears, the carrier detection becomes "0", so the transmission operation is started and ENQ is sent to establish the link with the center device. At this time, the CD holding time of the terminal # 1 is set to long t2.

[0019]

As described above, according to the present invention, since each terminal has a CD holding circuit which normally has a long holding time and can be switched to the shorter holding time by the data transmission signal of its own terminal, The carrier disconnection period during communication,
It is possible to prevent other terminals from recognizing that the line is idle and to eliminate the communication interruption so that the response of the center apparatus to the terminal which is transmitting data is not delayed and the serviceability of the system is improved.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of a data transmission control system of the present invention.

FIG. 2 is a diagram showing an embodiment of a data transmission control system of the present invention.

FIG. 3 is a transmission sequence according to the present invention.

FIG. 4 is a configuration diagram of a data transmission system targeted by the present invention.

FIG. 5: Transmission sequence in the prior art

[Explanation of symbols]

1,1-1 to 1-3 ... Terminal, 2 ... Center device, 3 ... Communication line,
11 ... Data transceiver, 16 ... Flip-flop, 17 ... CD
Holding circuit, 18 ... Carrier detector

Claims (1)

[Claims] 1. A plurality of center devices (2) are connected to the center device (2) through a multi-drop type communication line (3) and perform data transmission to the center device (2) by a contention method. In the system consisting of the terminal (1), the carrier detection unit (18) that detects the vacancy of the communication line (3) and outputs OFF to each terminal (1), and the carrier detection unit (18)
Is provided with a CD holding circuit (17) for outputting a CD signal which remains on for a predetermined time even after the output of the CD holding circuit is turned off, and during the data transmission from the own terminal, the CD holding circuit (17) By controlling the holding time to be shortened, the terminal that is transmitting data can detect the vacancy of the communication line earlier than other terminals and send the next data block with priority over other terminals. Data transmission control method.