JP5752054B2 - Receiving unit for digital communication device, digital communication device and digital communication system - Google Patents

Description

  The present invention relates to a receiving unit for a digital communication device, a digital communication device, and a digital communication system, and in particular, a receiving unit for a digital communication device provided for at least one of a plurality of communication terminals connected to a network, The present invention relates to a digital communication apparatus and a digital communication system.

  Conventionally, there is a standard called RS-485 as one of serial communication standards standardized by the American Electronic Industries Association. This standard is compatible with bus-type multipoint connection, and can be adopted in a digital communication system with a plurality of connections of up to 32 units. A digital communication device constituting this kind of digital communication system is provided with a communication interface called an RS-485 transceiver including an active element.

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  However, the RS-485 transceiver is a relatively expensive device because it contains active elements. For this reason, there is a problem that the cost of the digital communication apparatus is increased, and the cost of the entire digital communication system is also increased.

  In addition, the RS-485 transceiver includes an active element, so that the power consumption is relatively large. For this reason, there is a problem from the viewpoint of running cost of the digital communication system.

  Therefore, the present invention provides a receiving unit for a digital communication device, a digital communication device, and a digital communication system, which are devised so that the communication interface is composed of only passive elements, and can be driven at low cost and with low power consumption. The task is to do.

In order to solve the above problems, a receiving unit for a digital communication device, a digital communication device, and a digital communication system of the present invention include:
An input connected to the network;
A first diode group connected in series in the forward direction to the input terminal;
A second diode group connected in series in the opposite direction with respect to the input end;
A coupling line between a point between the diodes constituting the first diode group and a point between the diodes constituting the second diode group;
An output terminal connected to the coupling line and connected to an input buffer provided outside the receiving unit main body for the digital communication device.

1 is a configuration diagram of a schematic digital communication system according to Embodiment 1 of the present invention. FIG. It is a graph which shows the voltage value in A point-D point of FIG. It is a circuit block diagram of the receiving unit 300 for digital communication apparatuses provided in the central communication apparatus 22 and the terminal apparatuses 24-27 of FIG. It is a graph which shows the voltage value in the point a and b of FIG. It is a circuit block diagram of the receiving unit 300 for digital communication apparatuses which concerns on Embodiment 2 of this invention.

DESCRIPTION OF SYMBOLS 10 Communication network 22 Central communication apparatus 24-27 Terminal apparatus 300 Reception unit 310 Input terminal 320 Capacitance element 330 1st diode group 340 2nd diode group 360 Input buffer 370 Output terminal

BEST MODE FOR CARRYING OUT THE INVENTION

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a configuration diagram of a schematic digital communication system according to Embodiment 1 of the present invention. FIG. 1 shows a so-called multidrop digital communication system. This communication system includes a wired I / O control communication network (hereinafter simply referred to as “network”) 10 typified by a programmable relay controller (PLC) network, and a center connected to the network 10. The communication device 22 includes terminal devices 24 to 27 that are multipoint connected to the central communication device 22 and have unique addresses set therein.

  The network 10 includes at least two lines such as a signal transmission line and a ground line. Moreover, although the four terminal devices 24-27 are illustrated in FIG. 1, the number of terminal devices may be more or less than this.

  FIG. 2 is a graph showing voltage values at points A to D in FIG. Here, the case where the voltage value of the signal output from the central communication device 22 to the network 10 is high is indicated by a high level voltage value, and the case where the voltage value of the signal is low is indicated by a low level voltage value. .

  Due to the voltage drop of the network 10 and the voltage drops of the terminal devices 24 to 27, the voltage value at the high level gradually decreases from the point A to the point D.

As an example, if the voltage value at the high level at point A is 7.0 V, for example,
The voltage value at the high level at point B is, for example, 6.2 V,
The voltage value at the high level at point C is, for example, 5.5V,
The voltage value at the high level at the point D is, for example, 5.0 V, and decreases in an inverse proportion.

  FIG. 3 is a circuit configuration diagram of the digital communication device receiving unit 300 provided in the central communication device 22 and the terminal devices 24-27 of FIG. As shown in FIG. 3, the digital communication device receiving unit 300 is provided with an input terminal 310 to which a signal transmission line of the network 10 is connected.

  For example, a capacitive element 320 that functions as a high-pass filter is connected to the input terminal 310 in series. The condition of the capacitor 320 may be determined as appropriate according to the frequency of the input voltage. The capacitive element 320 may be connected in series to an input end (not shown) on the ground line side of the network 10, or may be connected to both the input end 310 on the signal transmission line side and the input end on the ground line side. Each element may be connected in series.

  A first diode group 330 is connected in series to the capacitive element 320 in the forward direction, and a second diode group 340 is connected in series in the reverse direction. The first diode group 330 divides the voltage input by the input terminal 310 to mainly set the voltage value at point b in FIG. 3 to a high level.

  On the other hand, in the second diode group 340, since the first diode group 330 has a considerable capacity, the charge stored in the capacity is caused to flow as a current toward the input terminal 310 side, so that The voltage at point b in 3 is returned to a low level.

  In the present embodiment, as the first diode group 330, for example, five diodes are shown. For example, the second diode group 340 includes two diodes. However, the numbers of diodes in the first diode group 330 and the second diode group 340 are examples, and are not limited thereto.

  The diodes 331 to 335, 341, and 342 may or may not have the same performance. However, as will be described later, the conditions of each of the diodes 331 to 335, 341, and 342 are that the voltage input by the input terminal 310 can be divided by each of the diodes 331 to 335, and the diode 332 to the diode 335. It is essential to allow a current to flow toward the diode and to allow a current to flow from the diode 341 toward the diode 342.

  Specifically, for example, as the voltage dividing condition, each of the diodes 331 to 335 may cause a voltage drop of 1 V, for example. Then, the voltage value at the point b in FIG. 3 is fixed to 4V because it is divided by the diodes 331 to 335 to 1: 4 when the voltage value at the point a is 5V or more.

  The diodes 331 and 332 constituting the first diode group 330 and the diodes 341 and 342 constituting the second diode group 340 are connected by a coupling line 350. The first diode group 330 and the second diode group 340 are both grounded through the diodes 335 and 341.

  In the case of FIG. 3, the coupling line 350 is connected between the diodes 331 and 332. However, for example, the coupling line 350 may be connected between the diodes 332 and 333. In this case, if the diodes 331 to 335 are composed of the same conditions, the voltage is divided by 2: 3 by the diodes 331 to 335 when the voltage value at the point a in the above example is 5 V or more. Therefore, it is fixed at 3V.

  An output end 370 is connected to the coupling line 350. The output terminal 370 is connected to an input buffer 360 provided outside the digital communication device receiving unit 300, such as a buffer with a Schmitt trigger provided inside the terminal device 24 or the like.

  Next, the operation of the digital communication device receiving unit 300 will be described. The digital communication device receiving unit 300 receives the voltage of the signal supplied from the network 10 at the input terminal 310. When the input voltage value is at a high level, a current flows through the first diode group 330 because the downstream side of the diode 335 is grounded.

  After that, when the value of the input voltage received at the input terminal 310 becomes a low level, the charge stored in the capacitor of the first diode group 330 becomes relatively low voltage at the input terminal 310, so that And flows to the second diode group 340.

  FIG. 4 is a graph showing voltage values at points a and b in FIG. Here, an example of the receiving unit 300 for the digital communication device built in the terminal device 24 is shown, and the case where the input voltage at point a becomes 5 V or more due to deformation due to external induction or reflected waves is shown. . In the description of FIG. 4, it is assumed that each of the diodes 331 to 335 causes a voltage drop of 1V.

  When the value of the input voltage received at the input terminal 310 is at a high level, that is, when the voltage value at the point a is 5 V or more, the voltage value at the point b becomes 4 V due to the voltage drop of the first diode group 330. For this reason, a voltage value lower than 4 V may be used as the high level side threshold (H) of the input buffer 360.

  Generally, this voltage value is 3.5V. Similarly, the low level threshold (L) of the input buffer 360 may be determined, and this voltage value is generally set to 0.8V.

  Even when a high voltage signal such as 10 V is input to the input terminal 310, the diodes 331 to 335 and 341 to 342 function as clippers. For this reason, since the high voltage value is clipped, the destruction of the input buffer 360 can be prevented.

  As a comparative example, the diodes 331 to 335 and 341 to 342 are not necessarily used if the input voltage input by the input terminal 310 is divided. A person skilled in the art would generally replace all of them as resistance elements.

  However, as described above, when the input voltage input by the input terminal 310 is a high voltage of 10 V, instead of the diodes 331 to 335 and 341 to 342, all of them are resistance elements, the input buffer There is a problem that a destructive voltage such as 8V is applied to 360.

  Moreover, if it replaces with each diode 331-335 and 341-342 and makes all of them into a resistive element, the amount of voltage drops in each resistive element will increase as the number of the terminal devices connected to the network 10 increases. become. Therefore, the input value of the input buffer 360 of the terminal device physically located far from the central communication device 22 falls below the threshold value, and communication is impossible.

  In other words, in order to divide the input voltage input by the input terminal 310, if all of them are used as resistance elements instead of the diodes 331 to 335 and 341 to 342, communication as a whole of the digital communication system is not disabled. In order to do so, there is also a problem that the number of terminal devices connected to the network 10 is limited.

  Therefore, in the present embodiment, instead of using a resistive element to divide the input voltage input by the input terminal 310, each of the diodes 331 to 335 and 341 to 342 is used to configure the digital communication device receiving unit 300. It is composed.

  However, it should be noted that it does not mention that a resistance element should not be used in the receiving unit 300 for the digital communication apparatus shown in FIG. As will be described later in the second embodiment, adding a resistance element under a certain condition to the first and second diodes 330 and 340 has various advantages.

  As is clear from the circuit configuration diagram of FIG. 3, the digital communication device receiving unit 300 is unique in this embodiment in that all of the elements are composed of passive elements. Therefore, unlike the conventional case, the digital communication device receiving unit 300 does not become expensive, and its power consumption is small.

(Embodiment 2)
FIG. 5 is a circuit configuration diagram of the receiving unit 300 for a digital communication apparatus according to the second embodiment of the present invention, and corresponds to FIG. In the present embodiment, a digital communication system that is suitable when the number of terminal devices increases or when the wiring length of the network 10 increases will be described.

  In FIG. 5, a resistor 336 is added to the first diode group 330 shown in FIG. 3, and a resistor 346 is added to the second diode group 340. In addition, the number of diodes in the first diode group 330 and the second diode group 340 is two, although illustrated.

  The resistors 336 and 346 may each be appropriately selected with a resistance value of several kΩ to several MΩ. Specifically, the resistance values of the resistors 336 and 346 are based on the noise intensity in the usage environment of the digital communication system and the minimum current value necessary for the digital communication device receiving unit 300 to operate the digital communication system. To select.

  In addition, each diode 332 and the like may be selected so as to sufficiently correspond to the frequency of the signal received at the input terminal 310. As this kind of diode, for example, a Schottky barrier diode can be selected, but is not limited thereto.

  5 shows a state in which the resistors 336 and 346 are connected downstream of the diodes 332 and 342, respectively, the resistors 336 and 346 may be connected upstream of the diodes 332 and 342. . Further, instead of adding both the resistors 336 and 346 to the first and second diode groups 330 and 340, only one of them may be added.

  Here, as the merit when only the resistor 336 is added to the digital communication device receiving unit 300, the following can be cited. That is, when the digital communication device receiving unit 300 receives the voltage of the signal supplied from the network 10 at the input terminal 310, when the input voltage value is at a high level, the current based on the voltage is digital as described above. The current flows to the first diode group 330 of the communication device receiving unit 300.

  However, although the current flowing through the first diode group 330 depends on the resistance value of the resistor 336, it is difficult to flow when viewed relatively. This is because the addition of the resistor 336 makes it difficult for current to flow through the first diode group 330.

  Further, if only the resistor 336 is added to the digital communication device receiving unit 300, the high level voltage value obtained at point b can be set to be the same as or higher than that in FIG. 3 by appropriately selecting the resistance value of the resistor 336. Can be a value.

  Therefore, as a merit when only the resistor 336 is added to the digital communication device receiving unit 300, the energy absorbed by the digital communication device receiving unit 300 from the signal waveform propagating through the network 10 is compared with that in FIG. It can be said that it can be made relatively small. In this embodiment, even if destructive noise is supplied to the point a, the energy reaching the point b is extremely small. Therefore, the destruction due to the destructive noise is avoided by a protection circuit that is provided as standard in the buffer 360.

  On the other hand, the merit when only the resistor 346 is added to the digital communication device receiving unit 300 is the same as when the resistor 336 is provided. That is, when the digital communication device receiving unit 300 receives the voltage of the signal supplied from the network 10 at the input terminal 310, the current flowing through the second diode group 340 decreases when the input voltage value is low. Therefore, the influence on the signal waveform propagating through the network 10 can be reduced.

  Further, as a merit when both resistors 336 and 346 are added to the receiving unit 300 for the digital communication apparatus, in addition to the above merits, the energy fluctuation to the signal waveform propagating through the network 10 is high level. Therefore, there is a merit that it is difficult to affect the signal waveform propagating through the network 10 at a low level. In particular, when the resistance values of the resistors 336 and 346 are approximated, the influence can be further suppressed.

Industrial application fields

  The present invention relates to medical equipment such as digital X-ray imaging apparatus and ultrasonic imaging apparatus, coin bill automatic payment machines such as cash register change machines and ATM apparatuses, OA equipment such as printers and scanners, vending machines such as tickets and drinking water. It can use suitably for the communication system of this.

Claims (5)

An input connected to the network;
A first diode group connected in series in the forward direction to the input terminal;
A second diode group connected in series in the opposite direction with respect to the input end;
A coupling line between a point between the diodes constituting the first diode group and a point between the diodes constituting the second diode group;
A digital communication device receiving unit comprising: an output end connected to the coupling line and connected to an input buffer provided outside the digital communication device receiving unit main body.   The receiving unit for a digital communication device according to claim 1, wherein a resistor is added to at least one of the first and second diode groups.   The digital communication device receiving unit according to claim 1, wherein a capacitive element is provided in series between the input terminal and the first and second diode groups. A digital communication device receiving unit according to any one of claims 1 to 3 and the external input buffer,
The input end is connectable to the network; and
A digital communication apparatus in which the output terminal is connected to the input buffer. A plurality of digital communication devices comprising the receiving unit for a digital communication device according to any one of claims 1 to 3,
A digital communication system comprising a network for connecting the digital communication devices to each other.

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