JPH08111674A - Insulated type interface circuit in half duplex serial transmission line - Google Patents

Abstract

PURPOSE: To obtain the insulated type interface circuit in a half duplex serial transmission line which is capable of electrically insulating the space between data transmitter and receiver in a serial transmission line and performing the transmission and reception of data by a single line. CONSTITUTION: When a digital signal is transmitted from a host 50 to a slave 52, the digital signals of H and L levels which are outputted from the host 50 drive a driver 32 via a switch circuit 54. As a result, a photocoupler 30 is made to perform an ON/OFF driving and the digital signals outputted from the host are outputted to a switch circuit 56 via the conversions of electricity - light - electricity. The switch circuit 56 transmits the digital signal outputted from the photocoupler 30 to the slave 52 without feedbacking the signal to the side of the host 50. When the digital signal is transmitted from the slave 52 to the host 50, the digital signal outputted from the slave 52 is transmitted to the host 50 via the switch circuit 56, a driver 36, a photocoupler 34 and the switch circuit 54 in this order, by the same procedure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulation type interface circuit in a half-duplex serial transmission line, and more particularly to an insulation type interface circuit in a half-duplex serial transmission line using means for optically relaying data transmission. .

[0002]

2. Description of the Related Art There are two types of data transmission methods between data transmitters / receivers, called parallel transmission and serial transmission. Further, depending on the direction of data transmission, they are unidirectional, full-duplex or half-duplex. Be divided. Especially half 2
The method called Shige has only one data transmission line,
Compared to full-duplex, which cannot send and receive data at the same time, it has a drawback, but it is economical because it has a small number of lines.

FIG. 2 shows a circuit diagram of a conventional half-duplex serial transmission system. In the figure, the line between the host 10 and the slave 12 is particularly shown. In the half-duplex serial transmission system shown in the figure, switching of transmission / reception in the host 10 and the slave 12 is performed by a transmission / reception switching signal output from a transmission / reception switching signal terminal. That is, when the transmission / reception switching signal of the host 10 is in the ON state, the driver 1
4 is in an operable state and the driver 16 is in an inoperable state so that data can be transmitted from the transmission data (Rxd) terminal and data cannot be received from the reception data (Txd) terminal. On the other hand, the transmission / reception switching signal is OFF
In the state, the driver 14 is inoperable, and the driver 1
6 becomes operable, data transmission from the Rxd terminal becomes impossible, and data reception from the Txd terminal becomes possible.

Contrary to the host 10, the slave 12 can receive data from the Rxd terminal when the transmission / reception switching signal is ON, and can transmit data from the Txd terminal when the transmission / reception switching signal is OFF. . As described above, data transmission / reception between the host 10 and the slave 12 is switched by the transmission / reception switching signal,
The data transmission from the slave 12 to the slave 12 and the data transmission from the slave 12 to the host 10 are performed by one line.

However, when the host and the slave are electrically connected by the data transmission line as in the half-duplex serial transmission line shown in FIG. 2, the electric noise generated in one device causes the other device to generate electrical noise. Will affect. In particular, when a power circuit such as a motor drive circuit is present on the slave side, the electrical noise on the slave side is large, and if this is transmitted to the host side, there is a problem that it will be adversely affected.

Further, the operating voltages on the host side and the slave side may be different, and there is a problem that the operation is unstable if they are electrically connected. FIG. 3 is a circuit diagram in which electrical isolation between the host side and the slave side is realized in order to solve these problems. As shown in the figure, photocouplers 30 and 34 are interposed in the data transmission line,
The electric signal output from the Txd terminal on the host side is once converted into an optical signal by the photodiode 30A of the photocoupler 30 via the driver 32. And
This optical signal is converted into an electric signal again by the phototransistor 30B and output to the Rxd terminal on the slave side. Similarly, the electric signal output from the Txd terminal on the slave side is converted into electric-optical-electricity by the photocoupler 34 and output to the Rxd terminal on the host side.

As a result, the host and the slave are electrically insulated from each other, and the above-mentioned problems of electrical noise and difference in operating voltage can be solved.

[0008]

However, in the line constructed as shown in FIG. 3, when the Txd terminal and the Rxd terminal are connected to unify the data transmission line as shown in FIG. 2, the line forms a loop. However, there is a problem in that they are formed and cause oscillation, latches, and the like. Therefore, in the line configured as shown in FIG. 3, it is not possible to make one data transmission line, and it is necessary to separately provide two data transmission lines and two reception lines. Furthermore, when the host and the slave are separated from each other, it is necessary to provide a common line, which requires three lines, which is not economical.

Recently, many devices such as EEPROMs are serially controlled, and in this type of device, it is general that the Txd terminal and the Rxd terminal are internally connected, as shown in FIG. There is a problem that the line cannot be used as it is. The present invention has been made in view of the above circumstances, and is an insulated interface in a half-duplex serial transmission line capable of electrically insulating between data transmitters and receivers and transmitting and receiving data by a single line. The purpose is to provide a circuit.

[0010]

To achieve the above object, the present invention provides a first data transmission line connected to a first data transceiver and a second data transmission line connected to a second data transceiver. Of the half-duplex serial transmission line arranged between the first data and the data transmission line of the first data. ON / OFF drive is performed based on the first data transmitted from the transceiver via the first data transmission line, and the first data is transmitted to the second data transceiver via the second data transmission line. The first photocoupler for transmitting data and the first photocoupler become operable when the output state of the first photocoupler is in the initial state, and are transmitted from the second data transceiver via the second data transmission line. First Is driven ON / OFF based on the data, the second transmitting the second data to the first data transceiver via the first data transmission line
And a first means for holding the output state of the second photocoupler in an initial state at the time of data transmission from the first data transceiver, and at the time of data transmission from the second data transceiver. Second means for holding the output state of the first photocoupler in the initial state.

[0011]

According to the present invention, at the time of data transmission from the first data transmitter / receiver, the first means holds the second photocoupler in the initial state, and the second photocoupler is transmitted via the first data transmission line. The first photo coupler is ON / OFF driven based on the first data, and the first data is transmitted to the second data transceiver via the second data transmission line.

On the other hand, at the time of data transmission from the second data transmitter / receiver, the first photocoupler is held in the initial state by the second means, and the second data is transmitted via the second data transmission line. Turn on the second photo coupler based on
It is turned on / off, and the second data is transmitted to the first data transceiver via the first data transmission line.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an insulating interface circuit in a half-duplex serial transmission line according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing an embodiment of an insulation type interface circuit in a half-duplex serial transmission line according to the present invention.

As shown in the figure, the interface circuit 60 is arranged between the data transmission path 62 on the host 50 side and the data transmission path 64 on the slave side. still,
The Txd terminal and the Rxd terminal of the host 50 and the slave 52 are short-circuited in the device. The interface circuit 60 mainly includes the photocouplers 30, 34, the driver 32,
36, and switch circuits 54 and 56.

As can be seen from these configurations, the circuits are symmetrically configured with respect to the two photocouplers 30 and 34. Therefore, in the following, the circuit related to the signal passing through the photocoupler 30 (that is, the signal transmitted from the host 50 side to the slave 52 side) will be mainly described. The photocoupler 30 includes a photodiode D1 that converts a current into light and a phototransistor Q4 that detects the light emitted from the photodiode D1 and converts the light into a current signal.

Photodiode D1 of photocoupler 30
Are connected to the DC power supply E1 between the emitter (E) and the collector (C) of the transistor Q1 forming the driver 32 and the resistor R1. When a current flows between the emitter (E) and the base (B) of the transistor Q1, a current is conducted between E and C (ON state), and a current is generated in the photodiode D1. As a result, the photodiode D1 emits light.

A switch circuit 54 is connected from the base of the transistor Q1 of the driver 32 via a resistor R2. The switch circuit 54 outputs a high level (H level) and a low level (L level) output from the host 50.
ON / OFF of the driver 32 based on the digital signal consisting of
Regarding the signal which is driven OFF and has passed through the photocoupler 34 at the time of data transmission from the slave 52 side, the host 5
It is a circuit that transmits only to 0.

That is, the switch circuit 54 prevents the data transmission line from forming a closed loop in the interface circuit 60 and causing oscillation and data latching. On the other hand, the phototransistor Q4 of the photocoupler 30
Is connected to a DC power source E2 via a resistor R5, and a voltage is constantly applied to the phototransistor Q4. Therefore, when no light is emitted from the photodiode D1, the phototransistor Q4 is turned off,
Collector terminal of phototransistor Q4 (terminal 5 in the figure)
Has the same potential as the DC power source E2.

When light is emitted from the photodiode D1, the phototransistor Q4 is turned on and a current flows from the DC power source E2. At this time, the resistance R5
The potential drop at the terminal 5 lowers the potential of the terminal 5. The change in the potential of the terminal 5 is changed through the switch circuit 56 in the same manner as the switch circuit 54 described above.
Be transmitted to.

Next, the operation of the above circuit when data is transmitted from the host 50 to the slave 52 will be described. The Txd terminal of the host 50 outputs H-level and L-level digital signals, but the voltage of the H-level signal is the same as that of the DC power supply E1. Therefore,
When an H level signal is applied from the Txd terminal of the host 50 to the switch circuit 54, both the transistors Q2 and Q1 are turned off because the H level signal and the voltage of the DC power source E1 are equal, and the photodiode D1 emits light. Does not happen.

As a result, no current flows through the phototransistor Q4, and the potential of the collector terminal (terminal 5 in the figure) of the phototransistor Q4 becomes the voltage of the DC power source E2. This potential is applied to the slave 52 via the resistor R6 of the driver 56.
It is added as it is to the Rxd terminal of. That is, the slave 52 has received an H level signal. On the other hand, when an L level signal is applied to the switch circuit 54 from the Txd terminal of the host 50, a voltage drop occurs at the resistor R3 because the L level signal voltage is lower than the voltage of the DC power source E1. That is, a forward voltage is applied between B and E of the transistor Q2. As a result, the transistor Q2 is turned on.

When the transistor Q2 is turned on, a forward voltage is applied between BE of the transistor Q1 of the driver 32 and the transistor Q1 is also turned on. As a result, the photodiode D1 emits light as described above. When the photodiode D1 emits light, the phototransistor Q4 is turned on by receiving the light from the photodiode D1.
Then, a current is generated in the phototransistor Q4.
At this time, a voltage drop occurs at R5, and the potential of the terminal 5 becomes lower than the above-described H level signal voltage (voltage of the DC power supply E2). This potential is directly applied to the Rxd terminal of the slave 52 via the resistor R6 of the switch circuit 56. That is, the slave 52 has received the L level signal.

When data is transmitted from the host 50 to the slave 52 as described above, the switch circuit 5
The transistor Q5 of 6 is always off,
The transistor Q6 of the driver 36 is held in the OFF state. As described above, the H and L level signals output from the host 50 are directly transmitted to the slave 52. Further, even when the slave 52 becomes the data transmitting side and the H and L level signals are output from the slave 52, this signal is transmitted to the host 50 as it is.

The interface circuit may be built in either the host or the slave, or may be independently provided on the data transmission line.

[0025]

As described above, according to the insulation type interface circuit in the half-duplex serial transmission line according to the present invention, an optical data transmission / reception path is provided to electrically insulate the data transmission / reception. As a result, electrical noise can be prevented from being transmitted through the data transmission path. Also,
It becomes possible to set the operating voltage for each data transceiver. Furthermore, by providing a simple transmission / reception switching circuit inside the insulation type interface circuit, it is possible to realize half-duplex serial transmission without the need to provide a complicated transmission / reception switching circuit inside the data transceiver.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an insulation type interface circuit in a half-duplex serial transmission line according to the present invention.

FIG. 2 is a circuit diagram of a conventional half-duplex serial transmission system.

FIG. 3 is a circuit diagram that realizes electrical insulation between a host side and a slave side.

[Explanation of symbols]

 30, 34 ... Photocoupler 32, 36 ... Driver 50 ... Host 52 ... Slave 54, 56 ... Switch circuit 60 ... Interface circuit

Claims (1)

[Claims] 1. A first connected to a first data transceiver
A half-duplex serial transmission line disposed between the second data transmission line and the second data transmission line connected to the second data transmitter / receiver. Becomes operable when the output state is the initial state, and is ON / OFF driven based on the first data transmitted from the first data transmitter / receiver via the first data transmission line, and the second data transmitter / receiver is operated. A first photocoupler for transmitting the first data to the second data transmitter / receiver via a data transmission line; and a first photocoupler which is operable when an output state of the first photocoupler is an initial state. ON / OFF drive is performed based on the second data transmitted from the second data transmitter / receiver via the second data transmission line, and the first data transmission / reception is performed via the first data transmission line. A second photocoupler for transmitting the second data, first means for holding the output state of the second photocoupler in an initial state during data transmission from the first data transceiver, Second means for holding the output state of the first photocoupler in the initial state during data transmission from the second data transceiver, and an insulating interface in a half-duplex serial transmission line. circuit.