JP7724654B2 - communication systems - Google Patents

Description

The present invention relates to a communication system using a multi-drop connection.

In communication systems that connect multiple communication devices, connection methods such as cascade connection and multi-drop connection are used. In such communication systems, identifiers such as addresses and IDs must be set when communicating between communication devices.

A cascade connection is a method of connecting communication devices in series. For example, a known method is to sequentially assign identifiers to the nearest child communication device from the parent communication device. However, if a child device along the path is turned off or malfunctions, information cannot be transmitted from that child device to downstream devices, preventing the setting of identifiers and reducing the reliability of communication.

On the other hand, a multi-drop connection is a 1:n connection, so information can be transmitted from the parent device to all child devices simultaneously. Therefore, even if one child device is turned off or malfunctions, it will not affect the other child devices.

Patent Document 1 describes a cascade-connected lighting control system that includes a relay that connects communication lines of the same polarity between slave units, and that maintains a closed state when power is cut off to the slave units, and maintains an open state when power is supplied to the slave units.

Patent No. 6089715

The method described in Patent Document 1 makes it possible to transmit information downstream in a cascade connection even if a specific slave device is powered off. However, if a relay fails or a slave device in the path is removed, information transmission downstream will still be impossible.

In multi-drop connections, identifiers are often set manually in advance on the device side, such as on the slave unit. This requires a large amount of configuration work and there is a risk of configuration errors, so it is desirable to automate identifier setting.

The present invention therefore aims to provide a communication system that can automatically set identifiers in a multi-drop connection.

The invention described in claim 1, which was made to solve the above problem, is a communication system in which a parent device and a child device are connected in a multi-drop manner, wherein the parent device comprises: a first fixed passive element connected to a voltage source that outputs a constant voltage; a first variable passive element connected to the voltage source and connected in parallel with the first fixed passive element; a second variable passive element connected in parallel with the first fixed passive element and in series with the first variable passive element; and a control unit that changes the impedance of the first variable passive element and the second variable passive element; a second fixed passive element having the same impedance as the first fixed passive element and connected in series with the first fixed passive element via a communication line; a detection unit electrically connected between the first fixed passive element and the second fixed passive element and the first variable passive element and the second variable passive element and detecting the voltage value between the connection points; and a setting unit setting its own identifier based on the detection result of the detection unit, wherein the first fixed passive element and the second fixed passive element and the first variable passive element and the second variable passive element form a bridge circuit.

According to the present invention, a bridge circuit is formed by a first fixed passive element, a second fixed passive element, and a first variable passive element, and a second variable passive element. This makes it possible to identify the connection position of the slave device within the network based on the voltage value of the detection unit connected to the midpoint of the bridge circuit, and to automatically set an identifier such as an ID.

1 is a configuration diagram of a communication system according to a first embodiment of the present invention. 2 is an equivalent circuit of the configuration shown in FIG. 1; FIG. 2 is a sequence diagram of communication between a parent device and a child device in the configuration of FIG. 1 . FIG. 4 is an explanatory diagram of a voltage pattern. 2 is a flowchart of a basic operation of the parent unit shown in FIG. 1 . 6 is a flowchart of the ID setting mode shown in FIG. 5. 2 is a flowchart of a basic operation of the slave unit shown in FIG. 1 . 8 is a flowchart of the ID setting mode shown in FIG. 7. 10 is a flowchart of an operation for automatically detecting the number of slave devices. FIG. 10 is a configuration diagram of a communication system according to a second embodiment of the present invention. 11 is an equivalent circuit of the configuration shown in FIG. 10.

(First embodiment)
A first embodiment of the present invention will be described below with reference to Figures 1 to 9. Figure 1 is a diagram showing the configuration of a communication system according to the first embodiment of the present invention.

The communication system 1 comprises a base unit 10 and multiple slave units 20. Figure 1 shows an example in which three slave units 20, slave unit 20A, slave unit 20B, and slave unit 20C, are connected in a multi-drop configuration. Of course, the number is not limited to three, as long as at least one slave unit 20 is connected. Also, although the configuration in Figure 1 appears to connect the slave units 20 sequentially, this is because signals are simply passed through the slave units 20 due to the fixed resistors 25 provided; no relaying is performed as in a cascade connection, and the connection topology is a multi-drop connection.

In this embodiment, a parent device refers to a communication device that sets an ID (identifier) for a child device in a communication system. A child device refers to a communication device that receives an ID from a parent device. Communication devices are not limited to devices that exclusively perform communication, but also include electronic devices with communication functions.

The parent device 10 and the child devices 20A, 20B, and 20C are connected in a multi-drop configuration via communication lines L1 and L2. The terminal child device 20C is connected to the parent device 10, forming a ring-shaped network, and a bridge circuit can be configured as described below.

The parent unit 10 includes a driver 11, a receiver 12, a determination unit 13, a setting unit 14, a voltage source 15, a fixed resistor 16, variable resistors 17 and 18, a current source 19, a detection unit 1A, and switching units 1B, 1C, 1D, and 1E.

The driver 11 outputs data to be transmitted from the parent device 10 to the child device 20 via communication lines L1 and L2. The receiver 12 receives data transmitted from the child device 20 to the parent device 10 via communication lines L1 and L2.

The determination unit 13 is composed of, for example, a microcomputer having a CPU (Central Processing Unit) and memory, and performs the ID setting operation described below.

The setting unit 14 is configured with a storage medium such as a memory, and the number of handset units is set by the handset number setting process described below. The number of handset units may also be set manually. In this case, the number of handset units is input via an input device (not shown) provided on the base unit 10, and the input number of handset units is set in the setting unit 14.

Voltage source 15 outputs a constant voltage. The positive (+) side of voltage source 15 is connected to one end of fixed resistor 16 and one end of variable resistor 17. The negative (-) side of voltage source 15 is connected to switching unit 1E and one end of variable resistor 18.

One end of the fixed resistor 16 is connected to the positive side of the voltage source 15, and the other end is connected to the switching unit 1C.

One end of variable resistor 17 is connected to the positive side of voltage source 15, and the other end is connected to switching unit 1C. One end of variable resistor 18 is connected to the negative side of voltage source 15, and the other end is connected to switching unit 1E. Variable resistors 17 and 18 have the same characteristics. The variable range of the resistance value of the variable resistor includes the range of 1 to n times (n is an integer) the resistance value of fixed resistor 16. This n indicates the maximum number of slave units 20 that can be connected.

Current source 19 outputs a constant current. One end of current source 19 is connected to switching unit 1C, and the other end is connected to switching unit 1E. Detection unit 1A detects the voltage across both ends of current source 19.

Switching unit 1B switches the connection destination of communication lines L1 and L2 leading to slave unit 20A between driver 11 and receiver 12 and an ID setting circuit consisting of voltage source 15, fixed resistor 16, variable resistors 17 and 18, current source 19, and detection unit 1A. When switching unit 1B selects the ID setting circuit, switching unit 1C switches the connection destination between fixed resistor 16 and variable resistor 17 and current source 19 and detection unit 1A.

Switching unit 1D switches whether communication lines L1 and L2 returning from terminal handset 20C are connected to the ID setting circuit. When switching unit 1D selects the ID setting circuit, switching unit 1E switches the connection destination between voltage source 15 and variable resistor 18, or current source 19 and detection unit 1A.

The slave unit 20 includes a driver 21, a receiver 22, a detection unit 23, a determination unit 24, and a fixed resistor 25.

The driver 21 outputs data to be transmitted from itself (child device 20) to the parent device 10 or another child device 20 via communication lines L1 and L2. The receiver 22 receives data transmitted from the parent device 10 or another child device 20 to itself (child device 20) via communication lines L1 and L2.

Detection unit 23 is provided between communication line L1 and communication line L2 and detects the voltage between communication line L1 and communication line L2. That is, detection unit 23 is electrically connected between fixed resistor 16 (first fixed passive element) and fixed resistor 25 (second fixed passive element) and variable resistor 17 (first variable passive element) and variable resistor 18 (second variable passive element), and detects the voltage value between the connection point to communication line L1 and the connection point to communication line L2.

The determination unit 24 determines and sets its own ID based on the voltage value detected by the detection unit 23. In other words, the determination unit 24 functions as a setting unit that sets its own identifier based on the detection result of the detection unit 23.

Fixed resistor 25 is provided on communication line L1. The resistance value of fixed resistor 25 is the same as that of fixed resistor 16. That is, fixed resistor 25 has the same resistance value (impedance) as fixed resistor 16 (first fixed passive element) and functions as a second fixed passive element connected in series with fixed resistor 16 (first fixed passive element) via communication line L1. That is, fixed resistor 16 functions as a first fixed passive element connected to voltage source 15. Furthermore, variable resistor 17 functions as a first variable passive element connected to voltage source 15 and connected in parallel with fixed resistor 16 (first fixed passive element). Furthermore, variable resistor 18 functions as a second variable passive element connected in parallel with fixed resistor 16 (first fixed passive element) and in series with variable resistor 17 (first variable passive element).

Next, the principle of ID setting in this embodiment will be explained with reference to Figure 2. Figure 2 is an equivalent circuit of the configuration shown in Figure 1. As shown in Figure 2, fixed resistors 16 and 25 are connected in series to communication line L1, and variable resistors 17 and 18 are connected in series to communication line L2.

The detection unit 23 of each slave unit 20 is connected between communication lines L1 and L2. Fixed resistors 16 and 25 have the same resistance value. Therefore, the circuit shown in Figure 2 can be configured as a Wheatstone bridge circuit by adjusting the resistance values of variable resistors 17 and 18.

The resistance values of variable resistors 17 and 18 are then sequentially changed to a resistance value that causes the voltage of detection unit 23 of handset 20A to be zero volts (0V), a resistance value that causes the voltage of detection unit 23 of handset 20B to be 0V, and a resistance value that causes the voltage of detection unit 23 of handset 20A to be 0V. The voltage value detected by detection unit 23 when the resistance value is changed is then retained, and the device's own ID is identified based on the change in the voltage value.

Figure 3 shows a sequence diagram of communication during ID setting operation between base unit 10 and handset 20A, handset 20B, and handset 20C in the configuration of Figure 1. In Figure 3, handset 20A and handset A are referred to as handset 20B, and handset 20C as handset C.

First, the parent device 10 sends an ID setting mode message to each child device 20 (T1). Because the communication system 1 is a multi-drop connection, the parent device 10 sends the ID setting mode message directly to each child device 20.

Next, the base unit 10 transmits the number of slave units N to each slave unit 20 (T2). In this embodiment, the number of slave units N = 3 is transmitted. Note that the number of slave units N may be detected automatically as described below, or may be manually set in advance in the base unit 10.

Next, the parent device 10 transmits a voltage change interval t to each child device 20 (T3). The voltage change interval t indicates the time interval at which the resistance values of the variable resistors 17 and 18 described above are changed. In this embodiment, it is set to 1 second, for example. By specifying this voltage change interval t, the detection unit 23 can measure the voltage value for the intended combination of resistance values.

Next, the ratio of variable resistor 17 (VR1) and variable resistor 18 (VR2) is set to VR1:VR2 = 1:3 as variable resistor setting 1 (T4). In this case, if the resistance value of fixed resistors 16 and 25 is R, then VR1 = R and VR2 = 3R are set. At this time, the voltage detected by detector 23 of handset A is Va1, the voltage detected by detector 23 of handset B is Vb1, and the voltage detected by detector 23 of handset C is Vc1.

Next, one second after variable resistor setting 1, variable resistor setting 2 is set so that the ratio of VR1 to VR2 is VR1:VR2 = 2:2 (T5). In this case, VR1 = 2R and VR2 = 2R. At this time, the voltage detected by the detector 23 of handset A is Va2, the voltage detected by the detector 23 of handset B is Vb2, and the voltage detected by the detector 23 of handset C is Vc2.

Next, one second after variable resistor setting 2, variable resistor setting 3 is set so that the ratio of VR1 to VR2 is VR1:VR2 = 3:1 (T6). In this case, VR1 is set to 3R and VR2 is set to R. At this time, the voltage detected by the detector 23 of handset A is set to Va3, the voltage detected by the detector 23 of handset B is set to Vb3, and the voltage detected by the detector 23 of handset C is set to Vc3.

Next, a voltage pattern is created in each handset 20 (T7). The voltage pattern will be explained with reference to Figure 4. Figure 4 is a diagram showing the voltage pattern detected in the sequence diagram of Figure 3. In Figure 3, the vertical axis represents voltage, and the horizontal axis represents each handset. That is, the left column represents the voltage value detected by the detection unit 23 of handset A, the center column represents the voltage value detected by the detection unit 23 of handset B, and the example on the right represents the voltage value detected by the detection unit 23 of handset C.

When variable resistor setting 1 is used, a balanced state is reached in which no current flows through the detector 23 of slave unit A, so Va1 becomes zero volts. If the voltage of voltage source 15 is V, then Vb1 becomes -1/4 V and Vc1 becomes -2/4 V.

When variable resistor setting 2 is selected, a balanced state occurs in which no current flows through the detector 23 of slave unit B, so Vb2 becomes zero volts. Va2 then becomes 1/4 V and Vc2 becomes -1/4 V.

When variable resistance setting 3 is used, an equilibrium state is reached in which no current flows through the detection unit 23 of child device C, and Vc3 becomes zero volts. Va3 becomes 2/4 V and Vb3 becomes 1/4 V. As is clear from Figure 4, changing the position at which the equilibrium state is reached results in different changes, with some child devices 20 changing their voltage pattern to the positive side, some changing their voltage pattern to the negative side, and some changing to both the positive and negative sides. In this embodiment, there are three child devices, so there are three rows; however, if there are four, there would be four rows, and if there are five, there would be five rows. Furthermore, due to the circuit characteristics, the child devices at both ends will be distributed from zero volts to the positive side or from zero volts to the negative side, and the child devices located in between will be distributed on either side of zero volts.

This voltage pattern is measured by each slave unit 20. Therefore, in reality, the voltage patterns measured by each slave unit 20 are not shown as a single graph as shown in Figure 4, but rather the portions corresponding to each column are measured by the corresponding slave unit 20.

Returning to the explanation of Figure 3, the slave device 20 identifies the device based on the voltage pattern detected by the detection unit 23, i.e., sets an ID (T8). In this embodiment, a slave device 20 whose voltage pattern is distributed on the positive side of a voltage of 0V is assigned ID=1, a slave device 20 whose voltage pattern is distributed on both the positive and negative sides of a voltage of 0V is assigned ID=2, and a slave device 20 whose voltage pattern is distributed on the negative side of a voltage of 0V is assigned ID=3. Such determination criteria are pre-set in the determination unit 24 of each slave device 20. In this embodiment, the number of slave devices N=3, but by having the determination unit 24 store correspondence between voltage patterns and IDs for N=1 to 64, for example, it is possible to accommodate a change in the number of slave devices, up to a maximum of 64.

Next, base unit 10 sends a confirmation message with ID=1 (T9). Upon receiving the message, handset A sends a response message back to the base unit (T10).

Next, base unit 10 sends a confirmation message for ID=2 (T11). Upon receiving the message, handset B sends a response message back to the base unit (T12).

Next, the base unit 10 sends a confirmation message for ID=3 (T13). Upon receiving the message, the slave unit C sends a response message back to the base unit (T14).

Next, the base unit 10 checks the total number of IDs (T15). In other words, it checks whether there have been responses to all messages in T9, T11, and T13. If there have been responses to all messages, it considers ID setting to be complete and resumes normal operation.

Next, Figures 5 to 8 show flowcharts of the operations of the parent unit 10 and the child unit 20 based on the above-described sequence. Figure 5 is a flowchart of the basic operations of the parent unit 10, which are mainly executed by the determination unit 13.

First, the parent unit 10 is powered on (S11). At this time, the determination unit 13 switches the switching units 1B to 1E so that the driver 11 and receiver 12 are connected to the communication lines L1 and L2. Next, the determination unit 13 transitions the parent unit 10 to ID setting mode (S12). At this time, as shown in Figure 3, an ID setting mode message is sent to each child unit 20. A flowchart of the ID setting mode in the parent unit 10 is shown in Figure 6.

In the ID setting mode in the base unit 10, the determination unit 13 first transmits the number of handset units N to the handset units 20 (S21). Here, a method for automatically detecting the number of handset units N (handset unit number setting process) will be described with reference to Figure 9. Figure 9 is an equivalent circuit for the configuration in Figure 1 when automatically detecting the number of handset units N. Note that the handset unit number setting process is not limited to being executed at the timing of S21, and may be executed at any timing.

In the circuit shown in Figure 9, the fixed resistor 25 of each slave unit 20 is connected in series to the current source 19. In other words, the determination unit 13 switches the switching units 1B to 1E so that the current source 19 and detection unit 1A are connected to the communication lines L1 and L2, replacing the voltage source 15, fixed resistor 16, and variable resistors 17 and 18.

If the constant current output from the current source 19 is I, the resistance value of the fixed resistor 25 is R, and the number of fixed resistors 25 (number of slave units) is N, the voltage V detected by the detection unit 1A is calculated using the following equation (1).
V=I×(N×R)...(1)

Transforming equation (1) yields the following equation (2).
N=V/(I×R)...(2)

Because the current value I and resistance value R are known, the determination unit 13 can determine the number of slave units based on the voltage value detected by the detection unit 1A using equation (2). In other words, the determination unit 13 functions as a calculation unit that calculates the number of slave units 20 based on the voltage across the current source 19. The calculated number of slave units N is set in the setting unit 14.

Returning to the explanation of Figure 6, after transmitting the number of slave devices N, the determination unit 13 transmits the voltage change interval t (S22). Upon completing S22, the determination unit 13 switches the switching units 1B to 1E so that the ID setting circuit is selected. However, the current source 19 and the detection unit 1A are not connected.

Next, the determination unit 13 varies the variable resistance value (S23). This corresponds to variable resistance settings 1 to 3 described in Figure 3. In other words, the ratio of the resistance values of the variable resistors 17 and 18 is changed, and the detection unit 23 of each slave unit 20 detects the voltage. In other words, the determination unit 13 functions as a control unit that varies the resistance value (impedance) of the variable resistors 17 and 18 (first variable passive element and second variable passive element). The determination unit 13 then varies the resistance value (impedance) of the variable resistors 17 and 18 (first variable passive element and second variable passive element) at predetermined time intervals by the number of slave units 20.

Next, the determination unit 13 determines whether the quantity is equal to N (S24). S24 is a step for changing the variable resistor setting by the quantity (number of times) of the number of slave units N. If the result of the determination in S24 is that the quantity is equal to N (S24; Yes), the ID setting mode ends. On the other hand, if the quantity is not equal to N (S24; No), the process returns to step S23 and the next variable resistor setting is made.

Returning to the explanation of Figure 5, when the ID setting mode ends, the determination unit 13 checks the number of child devices (S13). Checking the number of child devices is intended to verify whether the ID was set correctly in S12, and corresponds to T9 to T15 in Figure 3.

Next, the determination unit 13 determines whether the number of child devices confirmed in S13 is N (S14). If the number of child devices is N (S14; Yes), normal operation is performed thereafter (S15). On the other hand, if the number of child devices is not N (S14; No), the process returns to S12 and the ID setting mode is executed again. Note that in FIG. 5, the ID setting mode is repeated multiple times unless the number of child devices reaches N in S14, but it is also possible to set an upper limit on the number of repetitions, for example. If the upper limit is exceeded, a message indicating an abnormal state may be output, or a log may be saved as an abnormal termination.

Next, the flowchart of the basic operation of the handset 20 will be explained with reference to Figure 7. The flowchart in Figure 7 is mainly executed by the determination unit 24.

First, the handset 20 is powered on (S31). Then, the determination unit 24 determines whether an ID has been set (S32). In other words, it determines whether an ID has already been set in the internal memory of the determination unit 24, etc.

If the result of the determination in S32 is that an ID has been set (S32; Yes), normal operation will be performed thereafter (S34). On the other hand, if an ID has not been set (S32; No), the determination unit 24 transitions the slave device 20 to ID setting mode (S33). A flowchart of the ID setting mode in the slave device 20 is shown in Figure 8.

In the ID setting mode in the slave unit 20, the determination unit 24 first receives the number of slave units N from the master unit 10 (S41). Next, the determination unit 24 receives the voltage change interval t from the master unit 10 (S42). Next, the determination unit 24 causes the detection unit 23 to measure the voltage (S43). This voltage measurement corresponds to the voltage detection Va1, etc. in Figure 3.

Next, the determination unit 24 determines whether the quantity is N (S44). S44 is a step for changing the variable resistor setting by the number of child devices N. If the result of the determination in S44 is that the quantity is N (S44; Yes), the determination unit 24 creates a voltage pattern such as that shown in FIG. 4 (S45). On the other hand, if the quantity is not N (S44; No), the process returns to step S43 and voltage measurement is performed using the next variable resistor setting.

After creating the voltage pattern, the determination unit 24 identifies the device (S46). That is, the determination unit 24 identifies and sets an ID based on the created voltage pattern. The setting method can be, for example, as described in Figure 3. That is, the determination unit 24 (setting unit) sets the ID (identifier) based on the number of slave devices 20 and the voltage value detected by the detection unit 23 when the resistance value (impedance) changes for the number of slave devices 20.

According to this embodiment, in a communication system 1 in which a base unit 10 and multiple slave units 20 are connected in a multi-drop configuration, the base unit 10 includes a fixed resistor 16 connected to a voltage source 15, variable resistors 17 and 18 connected to the voltage source 15 and connected in parallel with the fixed resistor 16 and in series with each other, and a determination unit 13 that changes the resistance values of the variable resistors 17 and 18. The slave unit 20 also includes a fixed resistor 25 having the same resistance as the fixed resistor 16 and connected in series with the fixed resistor 16 via the communication line L1, a detection unit 23 electrically connected between the fixed resistors 16 and 25 and the variable resistors 17 and 18 and detecting the voltage value between the connection points, and a determination unit 24 that sets its own ID based on the detection result of the detection unit 23. The fixed resistors 16 and 25 and the variable resistors 17 and 18 form a Wheatstone bridge circuit.

By configuring the communication system 1 as described above, it becomes possible to identify the connection position of the slave device 20 itself within the network based on the voltage value of the detection unit 23 connected to the midpoint of the Wheatstone bridge circuit, and to automatically set the ID.

Furthermore, the determination unit 13 of the base unit 10 transmits the number N of slave units connected to the base unit 10 to the slave unit 20 in advance, and changes the resistance values of the variable resistors 17 and 18 N times at voltage measurement time intervals t. The determination unit 24 sets the ID based on the number N of slave units and the voltage values detected by the detection unit 23 when the resistance value changes multiple times. This makes it possible to obtain a voltage pattern that plots voltage changes. By obtaining a voltage pattern, the base unit's position can be accurately determined based on a pattern that distributes on the positive side, a pattern that distributes on the negative side, or a pattern that distributes on both sides of zero volts. Furthermore, by creating a voltage plot consisting of multiple measured voltages, a distribution based on zero volts can be created, ensuring the reliability of the measured voltage.

Furthermore, fixed resistors 16 and 25 are connected to communication line L1, which connects parent unit 10 and multiple child units 20, and variable resistors 17 and 18 are connected to communication line L2. Therefore, a Wheatstone bridge circuit can be configured using communication lines L1 and L2 to set the ID. Furthermore, using communication lines L1 and L2 allows for both control and voltage measurement, simplifying the configuration.

The base unit 10 also includes a current source 19 that is connected in series with the fixed resistor 25 via the communication line L1 and outputs a constant current, and a detection unit 1A that calculates the number of slave units 20 based on the voltage across the current source 19. This makes it possible to determine the number of slave units N from the number of fixed resistors 25 connected in series.

In addition, the first fixed passive element and the second fixed passive element are configured as fixed resistors, and the first variable passive element and the second variable passive element are configured as variable resistors, allowing for a simple circuit configuration.

Second Embodiment
Next, a communication system according to a second embodiment of the present invention will be described with reference to Figures 10 and 11. Note that the same parts as those in the first embodiment described above are denoted by the same reference numerals and description thereof will be omitted.

A communication system 1' according to this embodiment is shown in Figure 10. The communication system 1' includes a base unit 10' and multiple slave units 20'. Figure 10 shows an example in which three slave units 20' are connected: slave unit 20A', slave unit 20B', and slave unit 20C'. Of course, the number is not limited to three, as long as one or more slave units 20' are connected.

The parent unit 10' and the child units 20A', 20B', and 20C' are connected in a multi-drop configuration via communication lines L1 and L2. Power is supplied to the child unit 20' from the voltage source 30 via power lines PL1 and PL2, which are provided separately from the communication lines L1 and L2. Like the communication lines L1 and L2, the power lines PL1 and PL2 are also connected 1:n to the voltage source 30, which serves as the power source.

The parent unit 10' includes a driver 11, a receiver 12, and a determination unit 13'.

The driver 11 outputs data to be transmitted from the parent unit 10' to the child unit 20' via communication lines L1 and L2. The receiver 12 receives data transmitted from the child unit 20' to the parent unit 10' via communication lines L1 and L2.

The determination unit 13' is composed of, for example, a microcomputer having a CPU (Central Processing Unit) and memory, and performs the ID setting operation described below. Note that in this embodiment, no variable resistor is provided, so the determination unit 13' does not control the variable resistor after transmitting the number of slave devices N to each slave device 20'. However, after setting the ID, it may verify whether the ID has been set correctly.

The slave unit 20' includes a driver 21, a receiver 22, a detection unit 23', a determination unit 24', a fixed resistor 25, and a power supply unit 26.

The driver 21 outputs data to be transmitted from itself (child unit 20') to the parent unit 10' or another child unit 20' via communication lines L1 and L2. The receiver 22 receives data transmitted from the parent unit 10' or another child unit 20' to itself (child unit 20') via communication lines L1 and L2.

Detection unit 23' is connected to power lines PL1 and PL2 and detects the voltage between power lines PL1 and PL2. That is, detection unit 23' is electrically connected between fixed resistor 25 (fixed passive element) and the negative side of voltage source 30, and detects the voltage value between the connection point to power lines PL1 and PL2.

The determination unit 24' determines and sets its own ID based on the voltage value detected by the detection unit 23'. In other words, the determination unit 24' functions as a setting unit that sets its own ID (identifier) based on the detection results of the detection unit 23'.

Fixed resistor 25 is provided on power line PL1. That is, fixed resistor 25 functions as a fixed passive element connected in series via power line PL1 to voltage source 30, which outputs a constant voltage and supplies power to handset 20'.

Power supply device 26 receives power from voltage source 30 via power lines PL1 and PL2. Power supply device 26 adjusts the power received from voltage source 30, such as by stepping down or stepping up, to the voltage value required within child device 20' and outputs it to child device 20'.

Voltage source 30 is a power supply device that supplies power to sub-unit 20' (sub-units 20A', 20B', and 20C'). Voltage source 30 outputs a constant voltage.

The termination device 40 includes a termination resistor 41. The termination resistor 41 is connected between the power lines PL1 and PL2 output from the terminal handset 20C'.

Next, the principle of ID setting in this embodiment will be explained with reference to Figure 11. Figure 11 is an equivalent circuit of the configuration shown in Figure 10. As shown in Figure 11, a fixed resistor 25 and a termination resistor 41 are connected in series to the power supply line PL1.

Since the voltage value of the voltage source 30 and the resistance values of the fixed resistor 25 and the termination resistor 41 are known, the connection position can be identified and the ID can be set by detecting the voltage division ratio of the fixed resistor 25 based on the number N of slave devices. In this embodiment, instead of using a voltage pattern, the ID can be set by having the determination unit 24' store the relationship between the ID and the detected voltage for each number N of slave devices.

According to this embodiment, a communication system 1' includes a base unit 10' and multiple slave units 20' connected in a multi-drop configuration. Each slave unit 20' includes a fixed resistor 25 connected in series with a voltage source 30 via a power line PL1 from the voltage source 30, which outputs a constant voltage to supply power to the slave unit 20'; a detection unit 23' electrically connected between the fixed resistor 25 and the negative terminal of the voltage source 30 and detecting the voltage value between the connection points; and a setting unit 24' that sets its own ID based on the detection result of the detection unit 23'.

By configuring communication system 1 as described above, it becomes possible to identify its own connection position using the voltage division ratio of the fixed resistors connected in series, and the ID can be set automatically. Note that this second embodiment can also use communication lines L1 and L2 instead of power lines PL1 and PL2. In other words, a fixed resistor can be installed on communication line L1, and the voltage division ratio can be detected based on the number of slave devices.

In the above two embodiments, resistors were used as passive elements, but other passive elements such as capacitors (C) and coils (L) may also be used. Furthermore, the current is not limited to direct current and may be alternating current.

Finally, we will explain representative technical fields to which the communication systems 1 and 1' according to the above-mentioned embodiments can be applied. First, there is a lighting system. For example, in road tunnel lighting, lighting fixtures (child units) are installed at predetermined intervals, and a control device (parent unit) is installed outside the tunnel. Here, each lighting fixture requires individual control, such as dimming control from the entrance to the interior and day/night dimming control, so communication takes place between the control device and the lighting fixture.

In such lighting systems, when installing new fixtures, it is possible to set IDs in advance for each fixture, but if the wrong fixture is installed, the actual installation location of a lighting fixture with a certain ID may differ from the installation location recognized by the control device. Furthermore, lighting fixtures are sometimes rotated to extend their lifespan, and resetting IDs and changing settings on the control device each time is a significant workload.

By applying the communication systems 1, 1' according to this embodiment, IDs are automatically set, reducing the workload when installing new devices or rotating them. Furthermore, the application is not limited to tunnels; it may also be road lighting such as streetlights. The lighting fixtures may be included in the slave unit 20 (20'), or may be connected separately to the slave unit 20 (20'). In other words, the slave unit 20 (20') may be configured as a lighting device, or may have a lighting device connected to it.

The second example is railway equipment. That is, the communication system 1 (1') is installed in a railway vehicle. For example, instead of a configuration in which one parent unit 10 and a child unit 20 (20') are installed in each vehicle per train, one parent unit 10 and multiple child units 20 (20') may be installed in each vehicle. Specific examples include vehicle control devices for splitting and merging vehicles and trains (automatically recognizing the number of cars in a train), door opening/closing control devices for opening and closing doors in each vehicle (opening and closing only specific doors), information provision devices for each vehicle (providing information only to specific guidance terminals), and individual control devices for interior lights in each vehicle (individually dimming the window side, aisle side, door opening/closing position, etc.). In the case of railways, the formation may change, and the device IDs change frequently, so the application of the communication system 1 (1') is highly effective.

Furthermore, the present invention is not limited to the above-described embodiments. In other words, those skilled in the art can implement various modifications in accordance with conventional knowledge without departing from the gist of the present invention. As long as such modifications still comprise the configuration of the communication system of the present invention, they are of course included within the scope of the present invention.

1, 1' Communication system 10, 10' Parent device 13, 13' Determination unit 15 Voltage source 16 Fixed resistor (first fixed passive element)
17 variable resistor (first variable passive element)
18 variable resistor (second variable passive element)
19 Current source 1A Detector 20, 20' Child unit 23, 23' Detector 24, 24' Determination unit 25 Fixed resistor (second fixed passive element)
30 Voltage source L1, L2 Communication line PL1, PL2 Power line

Claims (7)

In a communication system in which a parent device and a child device are connected in a multi-drop manner,
The parent device is
a first fixed passive element connected to a voltage source that outputs a constant voltage;
a first variable passive element connected to the voltage source and connected in parallel with the first fixed passive element;
a second variable passive element connected in parallel with the first fixed passive element and in series with the first variable passive element;
a control unit that changes the impedance of the first variable passive element and the second variable passive element,
The slave unit is
a second fixed passive element having the same impedance as the first fixed passive element and connected in series with the first fixed passive element via a communication line;
a detection unit electrically connected between the first fixed passive element and the second fixed passive element and the first variable passive element and the second variable passive element, and configured to detect a voltage value between the connection points;
a setting unit that sets its own identifier based on the detection result of the detection unit,
the first fixed passive element and the second fixed passive element, and the first variable passive element and the second variable passive element form a bridge circuit;
A communication system comprising: the control unit transmits the number of the slave units connected to the control unit to the slave unit, and then changes the impedance of the first variable passive element and the second variable passive element by the number of the slave units at predetermined time intervals;
the setting unit sets the identifier based on the number of the slave units and a voltage value detected by the detection unit when the impedance changes by the number of the slave units.
2. The communication system according to claim 1. The communication system described in claim 2, characterized in that the control unit verifies whether each identifier has been set correctly after the setting unit sets the identifier. The parent device is
a current source connected in series with the second fixed passive element via the communication line and outputting a constant current;
a calculation unit that calculates the number of the slave units based on the voltage across the current source;
4. The communication system according to claim 1, further comprising: the first fixed passive element and the second fixed passive element are constituted by fixed resistors,
the first variable passive element and the second variable passive element are configured by variable resistors;
5. A communication system according to claim 1, wherein the communication system comprises: 6. The communication system according to claim 1 , wherein the slave unit is configured by a lighting device or is connected to a lighting device. 6. The communication system according to claim 1 , wherein the master unit and the slave unit are provided in a railway vehicle.