JPH04137939A - Electronic device of back board structure - Google Patents

Abstract

PURPOSE:To realize isolation among slots at a low cost by arranging a diode whose forward voltage drop is larger than that of a photocoupler of a slave circuit in parallel with a light emitting element of the photocoupler at a slot of a master circuit. CONSTITUTION:When a slave circuit 14 is connected to a slot 13, a current flows to a photocoupler 15 automatically. In this case, diodes 11, 12 are interrupted. Moreover, when a slave circuit 14 is disconnected, the current flows automatically to the diodes 11, 12 and gives not effect on a current loop. On the other hand, since a slave circuit is not mounted to a slot 33, the current flows to diodes 31, 32. When a slave circuit is mounted to the slot 33, the current flows to a photocoupler in the slave circuit automatically. Thus, even when a circuit is inserted/withdrawn to/from the slot of the back board, the current from a master circuit M is switched automatically without giving any effect on other circuit portions.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an electronic device having a backboard structure for transmitting and receiving digital signals.

<Prior Art> In order to send and receive digital signals via a serial bus, a plurality of slave circuits are sometimes mounted in slots on a backboard of a master circuit to form a current loop through serial transmission.

In such a case, as shown in Figure 2, an isolation transformer T is installed in each slave circuit to achieve isolation for each slot.
(T, ~Tn).

<Problem to be solved by the invention> However, since this method uses a transformer,
There is a problem that the cost of parts increases.

Additionally, the driver/receiver in each slave circuit is also expensive.

On the other hand, if isolation is to be achieved without using a transformer, there is a method of serial transmission using a backboard using a photocoupler as shown in FIG.

However, with this method, it is necessary to short-circuit terminal J in slots where no slave circuit is mounted in order to avoid affecting the current loop. In this case, since the third slot is not connected, the terminal J3 is short-circuited.

Therefore, there was a drawback that the slot could not be inserted or removed with a live wire. Additionally, troubles may occur due to incorrect settings or forgotten settings.

The present invention has been made to solve the above-mentioned problems, and its purpose is to provide an electronic device equipped with a current loop type serial transmission path in which a slave circuit is mounted in a slot on a backboard of a master circuit. Hot-line insertion and removal is possible, and there is no need for configuration elements to indicate whether each slot is installed or not.
The objective is to realize an electronic device with a backboard structure in which insulation of each slot can be realized at low cost.

<Means for Solving the Problems> The present invention, which solves the above-mentioned problems, includes a slave circuit mounted in each of a plurality of slots on a backboard of a master circuit, and a photocoupler for transmitting a digital signal from the master circuit to the slave circuit. In the electronic device that performs serial transmission using the current loop method, a diode with a higher forward voltage drop than the photocoupler of the slave circuit is placed on the slot side of the master circuit in parallel with the light emitting element of the photocoupler. This is a characteristic feature.

Effect> In the electronic device with the backboard structure of the present invention, when the slave circuit is connected to the slot of the master circuit, the signal current flowing through the diode of the slot flows through the light emitting element of the photocoupler of the slave circuit. As a result, digital signals from the master circuit are serially transmitted to the slave circuit. On the other hand, when the slave circuit is removed from the slot, the signal current flows through the slot's diode and does not affect other parts of the Karen I loop.

<Examples> Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic structure of an embodiment of the present invention. For the purpose of explanation, a case where eight slave circuits can be connected to a master circuit will be described here.

In this figure, a master circuit M has a transmitter T that transmits a digital signal to a slave circuit, and a receiver circuit R that receives a digital signal from the slave circuit. Backboard B consists of a transmission line and a reception line.

11.12 is a diode placed in series on the transmission line from the master circuit, 13 is a slot, and 14 is a slot 13.
Slave circuit connected via 15 is diode 1
．． A photocoupler 1.12 is connected in parallel to receive the digital signal from the transmitting section T, and 16 is a photocoupler connected to the receiving line for sending the digital signal to the receiving section R. In the circuit shown in this figure, a total of 118 sets of such diodes and slots are arranged.

The operation of such a device is as follows.

A digital signal is serially transmitted from the transmitter T of the master circuit M using a constant current current loop method. That is, a transmission signal given from a circuit (not shown) is converted into a constant current signal by the transistor Ql, the Zener diode ZD, and the transistor Q2. Then, it flows through the transmission path of backboard B. Here, when a light emitting diode is used as the diode 11°12~81.82 in the transmission path, the voltage drop V at normal operating current is 1.5V.
/ piece, so there is a voltage drop of 3μ between two pieces. Also,
The voltage drop of the photocoupler in the slave circuit connected in parallel with this diode is 1.5V. Therefore, when the slave circuit 14 is connected to the slot 13, current automatically flows through the photocoupler 15.

At this time, diodes 11 and 12 are in a cut-off state. Also, when the slave circuit 14 is removed, the current automatically flows through the diodes 11, 12 without affecting the current loop. This is the other slave circuit 2
The same goes for 4.44.84.

On the other hand, since no slave circuit is mounted in the slot 33, current flows through the diodes 3 and 32. Here, when a slave circuit is mounted in the slot 33, current automatically begins to flow through the photocoupler in the slave circuit.

Therefore, even if the backboard slot is inserted or removed, it will not affect other parts at all! The current from the master circuit M is automatically switched without any interruption. As a result, a constant current loop circuit is formed depending on the presence or absence of the slave circuit. This eliminates the need for setting elements depending on the connection state of the slave circuit. Therefore, troubles caused by incorrect settings or forgotten settings can be prevented.

In the above embodiment, the light emitting diodes are connected to the backboard side in two rows, but the invention is not limited to this. For example, the diode on the backboard side may be an element that has a larger voltage drop than the forward voltage drop V of the light emitting diode in the photocoupler.

<Effects of the Invention> As explained in detail above, in the present invention, a slave circuit is mounted in each of a plurality of slots on a backboard of a master circuit, and a digital signal is transmitted from the master circuit to the slave circuit using a photocoupler. In an electronic device that performs serial transmission using a current loop method, a diode having a larger forward voltage drop than a photocoupler in a slave circuit is placed on the slot side of a master circuit in parallel with the light emitting element of the photocoupler. .

Therefore, in the electronic device with the backboard structure of the present invention, when the slave circuit is connected to the slot of the master circuit, the signal current flowing through the diode of the slot flows through the light emitting element of the photocoupler of the slave circuit. As a result, digital signals from the master circuit are serially transmitted to the slave circuit. On the other hand, when the slave circuit is removed from the slot, the signal current flows through the slot's diode and does not affect other parts of the current loop. As a result, it is possible to realize an electronic device with a backboard structure that allows insertion and removal with a live wire, does not require a setting element to indicate whether each slot is mounted or not, and can realize insulation of each slot at low cost.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of an electronic device with a backboard structure according to an embodiment of the present invention, Fig. 2 is a block diagram of an electronic device with a conventional backboard structure, and Fig. 3 is a block diagram showing the configuration of an electronic device with a conventional backboard structure. FIG. 7 is a configuration diagram showing another configuration example of the electronic device. M...Master circuit T...Transmission section R...Reception section B...Backboard 1], 12.
・Diode 13...Slot 14 Slave circuit 15...
Photocoupler 16 for reception...Photocoupler 21, 22 for transmission...Diode 23...Slot 24 Slave circuit 25...
・Photocoupler 26 for reception...Photocoupler 31, 32 for transmission...Diode 33...Slot 4] 42...Diode 43...Slot 44 Slave circuit 45...
・Photocoupler 46 for reception...Photocoupler 81, 82 for transmission...Diode 83...Slot 84 Slave circuit 85...
・Photocoupler 86 for reception...Photocoupler for transmission Patent applicant: Yokogawa Electric Corporation

Claims (1)

[Claims] An electronic device in which a slave circuit is mounted in each of a plurality of slots on a backboard of a master circuit, and serially transmits a digital signal from the master circuit to the slave circuit by a current loop method using a photocoupler. An electronic device having a backboard structure, characterized in that a diode having a larger forward voltage drop than a photocoupler in a slave circuit is arranged on a slot side of a master circuit in parallel with a light emitting element of the photocoupler.