JPH04304740A - Two-wire current loop multi-drop transmission circuit - Google Patents

Abstract

PURPOSE:To improve a problem that the transmission of all slave sets is stopped due to a fault of one slave set in a current loop having been made up of series connection of, e.g. photocoupler series circuits of a master set and slave sets in the transmission circuit for the master set and the plural slave sets each having the photocoupler series circuit in which a photo transistor of a transmission photocoupler and a photodiode of a reception photocoupler are connected in series. CONSTITUTION:Transmission circuits L1-Ln of slave sets S1-Sn are connected in parallel with a transmission line L of a master set M, the slave sets S1-Sn turn on a transmission photocoupler 2T in the standby state and the master set turns on/off the transmission photocoupler 2T to designate the slave set in the transmission opposite party. Then other slave sets than the relevant slave set turn off the transmission photocoupler 2T for a prescribed time and the master set turns on the transmission photocoupler 2T for that time and the relevant slave set is turned on/off to send a data to the master set.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a circuit in which a parent unit and a plurality of slave units are connected in a multi-drop manner to a two-wire current loop, and performs 1:n half-duplex transmission via this current loop. This invention relates to a two-wire current loop multi-drop transmission circuit. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

0002

[Prior Art] For example, automatic meter reading using an automatic meter reading electricity meter (hereinafter referred to as "watt hour meter") that functions as a meter for automatic meter reading and an automatic meter reading consumer terminal (hereinafter referred to as "transmission terminal device") In the system, one-to-one transmission is performed between the watt-hour meter and the transmission terminal using a two-wire unidirectional current loop using a photocoupler. It is insulated by a photocoupler and does not require an isolated power supply for transmission on the watt-hour meter side.

FIG. 3 shows the basic configuration of such a power supply loop. In the figure, M is the main unit as a transmission terminal;
S is a slave unit as a power meter, 2T is a master unit M and a slave unit S, respectively.
A photocoupler 2R for transmission is provided in the base unit M and a photocoupler for reception is provided in the slave unit S. In this master unit M, the phototransistor PT of the transmitting photocoupler 2T and the photodiode PD of the receiving photocoupler 2R are connected in series with a polarity that allows current to flow, and the slave unit S
The transmitting photocoupler 2T and receiving photocoupler 2R are also connected in the same way. The series circuit of the photocouplers 2T and 2R of the master unit M and slave unit S is connected to the transmission DC power supply 1.
, and the current limiting resistor 3 in series with a polarity that allows current to flow, forming a loop-shaped transmission circuit L.

[0004] Here, the transmitting photocoupler 2T of the main unit M is
N. When the transmitting photocoupler 2T of the slave unit S is also turned on, a transmission circuit L is formed by the power supply loop. When transmitting data from the master unit M to the slave unit S, the transmitting photocoupler 2T of the slave unit S is
By turning on/off the transmitting photocoupler 2T of the base unit M in response to the data to be sent to the slave unit S while keeping T on, the receiving photocoupler 2R of the slave unit S is turned on/off.
F, and the slave unit S can receive data. The same goes for transmission from the slave unit to the base unit.

When a plurality of power meters (slave units) S (S1 to Sn) are connected to a transmission terminal (master unit) M using the above-mentioned current loop method to perform one-to-n transmission, the following is described. The following connection configurations are possible. (2) The number of transmission ports is set equal to the number of power meters S1 to Sn connected to one transmission terminal M, and the number of transmission circuits is L1 to Ln (see FIG. 4). (2) Connect the watt-hour meters S1 to Sn to which addresses have been given in series to one transmission circuit L from the transmission terminal M (see FIG. 5).

[0006]

[Problem to be Solved by the Invention] In transmission in which a plurality of slave units S are connected to one base unit M, the slave units S1 to Sn connected to one base unit M are Providing as many transmission ports as the number of transmission ports requires wiring and hardware for the number of transmission ports, resulting in a complicated structure and high cost. When the slave units S1 to Sn are connected in series to the transmission circuit L from the terminal, there is a problem that if there is a slave unit S whose power is cut off, the current loop L will not be established and transmission will be impossible. Therefore, it is an object of the present invention to provide a two-wire current loop multi-drop transmission circuit that can solve these problems.

[0007]

[Means for Solving the Problems] In order to solve the above problems, a transmission circuit according to claim 1 uses a transmission photocoupler (2T
etc.) phototransistor and receiving photocoupler (2R
A circuit formed by connecting a photodiode (e.g.) in series with a polarity that allows current to flow (hereinafter referred to as a photocoupler series circuit)
A master unit (such as M) and multiple slave units (S (S1, etc.) each have
~Sn), etc.), the photocoupler series circuit of the child device is connected in parallel with the same polarity, and at least this parallel circuit, the photocoupler series circuit of the parent device, and a transmission DC power source (such as 1) are provided. Connect in series and in a loop with a polarity that can conduct electricity,

In the transmission circuit according to claim 2, in the transmission circuit according to claim 1, during standby, each of the slave units turns on its own transmitting photocoupler, and the base unit turns on its own transmitting photocoupler. Make sure to turn it off and specify at least the address of the slave device with which you want to communicate, and

00
[09] In the transmission circuit according to claim 3, in the transmission circuit according to claim 2, when the address of the slave unit is specified, other slave units other than the slave unit use their own transmission photocouplers. The device is turned off for a predetermined period of time, and within this time, at least the base device turns on its own transmission photocoupler, and the slave device turns on and off its own transmission photocoupler to transmit data to the base device. do it like this.

0010

[Operation] Connects between the base unit M and slave units S1 to Sn.
The slave units S1 to Sn are connected in parallel to the transmission circuit L from the base unit, and data (address) for selecting the slave unit from the base unit.
A transmission procedure is adopted in which the unselected slave units are disconnected from the transmission circuit, and only the selected slave units transmit data to the base unit.

[0011]

[Embodiment] An embodiment of the present invention will be described below based on FIGS. 1 and 2. FIG. 1 is a block diagram of a transmission circuit as an embodiment of the present invention. In the same figure, S (S1 to Sn) refers to multiple slave units (S1 is referred to as #1 slave unit, and Sn is referred to as #n slave unit).
The transmission circuits L1 to Ln of the slave units S1 to Sn are connected in parallel to the transmission circuit L of the master unit M. In FIG. 1, first, the value of the current flowing from the master unit M to the transmission circuit L is the maximum value of the current that can be passed through one unit on the slave unit S side. Therefore, the number of connectable slave units S is determined by the current flowing out from the master unit M from each slave unit S1 to
The value of the shunt to Sn becomes the limit number of shunts that can exceed the minimum value of the current guaranteed to turn on the receiving photocoupler 2R of the slave unit S.

Next, the transmission procedure between the base unit M and the slave units S1 to Sn will be described. (1) Give different addresses to all slave units S1 to Sn. (2) When not in the transmission state, the transmitting photocoupler 2T of the base unit M is OFF, and the transmitting photocouplers 2T of the slave units S1 to Sn are in the ON state. (3) Transmission between the master device M and the slave devices S1 to Sn is performed as follows. Note that FIG. 2 is a time chart for explaining this transmission, and the transmission method will be explained below based on this FIG. 2.

(2) At the start of transmission, base unit M turns on its own transmitting photocoupler 2T for a certain period of time t1. ■Slave unit S
1 to Sn, the own receiving photocoupler 2R is connected for a certain period of time t
If it is ON for 2 (t2<t1) or more, the receiving state is set. (2) First, the master device M transmits transmission data DM (DM1) including the address of the #1 slave device S1. ■Slave units S1 to Sn receive transmission data DM1 from base unit M, and if the address in this transmission data matches the address given in advance, then the slave units S (in this case, #1 slave unit first S1) determines that it has been selected, waits for a certain period of time t3 from the end of data reception from the base unit M, and then downloads the data DS corresponding to the data DM1 received from the base unit.
(DS1) is transmitted to base unit M.

[0014] Other handsets S whose addresses do not match, for a certain period of time t4 from the end of receiving the transmission data from the master,
Turn off its own transmitting photocoupler 2T and disconnect it from its own transmission circuit L. ■The base unit M is in the reception state for a certain period of time t5 after the end of transmission from itself (the transmission photocoupler is turned off)
N) and receives data DS1 from slave device S1. After this time t5, the base unit M transmits the transmission data DM (DM2) to the next slave unit S2, repeats the same procedure as above, and from this slave unit S2 transmits the transmission data DS (DS2).
). Thereafter, the same communication is repeated in order for the remaining slave units S3 to Sn. In this way, when the base unit M runs out of data to be transmitted to all slave units S1 to Sn, it turns off its own transmission photocoupler 2T.
Let it be F. ■If the receiving photocoupler 2R of itself is OFF for a certain period of time t2 or more, the handset S enters the reception standby state (
The transmitting photocoupler 2T of the handset itself is ON).

[0015]

[Effects of the Invention] According to the present invention, the transmitting photocoupler 2T
A master unit M and a plurality of slave units S (S1 to Sn),
The photocoupler series circuits of the child units S1 to Sn are connected in parallel with the same polarity, and at least this parallel circuit, the photocoupler series circuit of the parent unit, and the transmission DC power supply 1 are connected in series with a polarity that allows energization. Since we configured a two-wire current loop multi-drop transmission circuit by connecting the two wires in a loop, there are two transmission lines and the slave unit does not have an insulated power supply for transmission. It is possible to perform highly reliable multi-drop half-duplex transmission in which the transmission of other handsets is not affected by the failure of one handset.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a transmission circuit as an embodiment of the present invention.

[Figure 2] Time chart for explaining the operation in Figure 1

[Figure 3] Explanatory diagram of current loop

[Fig. 4] A diagram showing an example of a conventional transmission circuit between a base unit and multiple slave units.

[Fig. 5] A diagram showing another example of a conventional transmission circuit between a base unit and multiple slave units.

[Explanation of symbols]

M Base unit S (S1~Sn) Child machine 1 DC power supply for transmission 2T Transmission photocoupler 2R Reception photocoupler 3 Resistance L Master unit transmission circuit L1~Ln　Slave unit transmission circuit

Claims (3)

[Claims] Claim 1: A base unit and a plurality of slave units each having a circuit formed by connecting a phototransistor of a transmitting photocoupler and a photodiode of a receiving photocoupler in series with a polarity that allows current to flow (hereinafter referred to as a photocoupler series circuit). , the photocoupler series circuit of the child unit is connected in parallel with the same polarity, and at least this parallel circuit, the photocoupler series circuit of the parent unit, and the transmission DC power supply are connected in series with a polarity that allows energization. A two-wire current loop multi-drop transmission circuit characterized by being connected in a loop. 2. The transmission circuit according to claim 1, wherein during standby, each of the slave units turns on its own transmitting photocoupler;
A two-wire current loop multi-drop transmission circuit, characterized in that the base unit turns on and off its own transmitting photocoupler to designate at least the address of a slave unit with which it communicates. 3. In the transmission circuit according to claim 2, when the address of the slave unit is specified, other slave units other than the slave unit turn off their own transmission photocouplers for a predetermined period of time; Within this time, at least the base unit turns on its own transmission photocoupler, and the slave unit turns on and off its own transmission photocoupler to transmit data to the base unit. Two-wire current loop multidrop transmission circuit.