JPH04344913A - Digital input insulation circuit - Google Patents

Abstract

PURPOSE:To obtain the input insulation circuit of a low consumption type for which power supply capacity need not be increased in accordance with the number of pieces of external contacts by providing a latch circuit which receives a command from an address decoder, and latches only the input circuit of the insulation circuit related to an input buffer the address decoder starts to control, and interrupts the input circuit of other insulation circuits. CONSTITUTION:The address decoder 4 commands the latch circuit 5 about the external contact whose opening and closing state is to be taken in. For instance, if it is a command of the effect that the opening and closing state of the external contacts SW0 to SW7 is to be taken in, the latch circuit 5 turns on a switching element 51, and turns off the switching elements 52 to 5n. Accordingly, only the input circuit of a photocoupler 21 is latched, and the input circuits of the photocouplers 22 to 2n are interrupted. Thus, since no current flows in the input circuits of the photocouplers 22 to 2n, current consumption is reduced, and consequently, the power supply capacity becomes needless to be increased in accordance with the number of pieces of the external contacts, and the input insulation circuit of the low consumption type is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital input isolation circuit used as an input circuit for a digital control device using a microcomputer.

0002

[Prior art] Figure 4 shows, for example, "transistor technology" CQ.
This is a circuit diagram showing a conventional digital input isolation circuit shown in the publication June 1986, page 343. In the figure, SW0 to SW8n-1 (n=1, 2, 3,...) are external contacts. The digital input isolation circuit captures the open/close state of the external contact so that a digital control device (not shown) or the like can recognize the open/close state of the external contact.

11 to 1n are current limiting resistors, and 21 to 2n are connected to input circuits (see FIG. 5) through which current flows when the external contacts SW0 to SW8n-1 are closed, and output digital signals depending on the presence or absence of the current. Photocoupler to output (
31 to 3n are input buffers for receiving digital signals from the photocouplers 21 to 2n and transmitting them to the data bus, and 4 is an input buffer for sequentially transmitting the digital signals output from the photocouplers 21 to 2n to the data bus. This is an address recorder that sequentially controls 31 to 3n.

Next, the operation will be explained.

First, a case will be described in which the open/closed states of the external contacts SW0 to SW7 are captured from the first photocoupler 21.

When the external contacts SW0 to SW7 are closed, the input circuit becomes a closed loop, so the photocoupler 21
A forward current flows through the photodiode, and the output side phototransistor is turned on. On the other hand, external contacts SW0~SW
7 is open, the input circuit becomes an open loop, so no forward current flows and the phototransistor is turned off.

Here, when the address recorder 4 outputs a chip select signal to control the input buffer 31,
The input buffer 31 opens its gate and transmits a digital signal corresponding to ON/OFF of the phototransistor in the photocoupler 21 to the data bus.

Further, as mentioned above, the open/closed states of the external contacts SW8 to SW8n-1 are also input to the other photocouplers 22 to 2n, so that the address recorder 4 sequentially controls the input buffers 31 to 3n. The open/close states of all external contacts SW0 to SWn are transmitted to the data bus.

[0009]

[Problems to be Solved by the Invention] Since the conventional digital input isolation circuit is configured as described above, when an external contact is in a closed state, the input circuit related to the external contact has a
A current of about ~20mA will flow (it is necessary to flow this much current to stabilize the switching of the photocoupler), and since it is necessary to consider the case where all external contacts are closed, it is necessary to There were issues such as the need to increase the power supply capacity depending on the number of contacts handled.

The present invention was made to solve the above-mentioned problems, and its purpose is to provide a low-consumption type digital input isolation circuit that does not require increasing the power supply capacity according to the number of external contacts. shall be.

[0011]

[Means for Solving the Problems] A digital input isolation circuit according to the present invention receives a command from an address recorder,
A latch circuit is provided that latches only the input circuit of the insulation circuit related to the input buffer that the address recorder starts controlling, and shuts off the input circuits of other insulation circuits.

0012

[Operation] The digital input isolation circuit in this invention has the following features:
The latch circuit latches only the input circuit of the insulation circuit related to the input buffer that the address recorder starts controlling, and cuts off the input circuits of the other insulation circuits, so that no current is consumed in the input circuits of the other insulation circuits.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a digital input isolation circuit according to an embodiment of the present invention. In the figure, the same reference numerals as those in the conventional circuit indicate the same or corresponding parts, and the explanation thereof will be omitted.

5 receives a command from the address recorder 4,
The address recorder 4 latches only the input circuits of the photocouplers 21 to 2n (photocoupler 21 for the input buffer 31) related to the input buffers 31 to 3n (for example, input buffer 31) that start control, and latches the input circuits of the other photocouplers 2
1 to 2n (photocoupler 22 for input buffer 31)
-2n) is a latch circuit that shuts off the input circuits, and 5a is a control unit that judges the command of the address recorder 4 and controls the switching elements (for example, photocouplers) 51-5n.

Next, the operation will be explained.

First, the address recorder 4 is connected to the latch circuit 5.
The external contact that should capture the open/closed state is commanded. For example, if the command is to capture the open/closed states of the external contacts SW0 to SW7, the latch circuit 5 turns on the switching element 51 and turns off the switching elements 52 to 5n. As a result, only the input circuit of the photocoupler 21 is latched, and the input circuits of the photocouplers 22 to 2n are cut off.

Next, after the operation delay time of the photocoupler 21, the address recorder 4 outputs a chip select signal to the input buffer 31, so that the input buffer 31 opens the gate and turns the phototransistor in the photocoupler 21 ON/OFF. A digital signal corresponding to the data bus is sent to the data bus.

In addition, other external contacts SW8 to SW8n-
1, the address register 4 is connected to the latch circuit 5 and the input buffer 32 in the same way as above.
~3n, all external contacts SW0
~The open/close status of SW8 is transmitted to the data bus. Note that FIG. 3 is a flowchart showing the operation of the digital input isolation circuit according to one embodiment of the present invention.

[0019]

As described above, according to the present invention, only the input circuit of the isolation circuit related to the input buffer that receives a command from the address recorder and which the address recorder starts controlling is latched, and the input circuit of the other isolation circuit A latch circuit is provided to cut off the power, so even if all external contacts are closed,
Since no current flows through the input circuit of the other insulation circuit, current consumption is reduced, and as a result, there is an effect that there is no need to increase the power supply capacity according to the number of external contacts.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a digital input isolation circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an input circuit of the digital input isolation circuit of FIG. 1;

FIG. 3 is a flowchart showing the operation of the digital input isolation circuit of FIG. 1;

FIG. 4 is a circuit diagram showing a conventional digital input isolation circuit.

FIG. 5 is a circuit diagram showing an input circuit of the digital input isolation circuit of FIG. 4;

[Explanation of symbols]

SW0 ~ SW8n-1 External contact 21~2n Photocoupler 31~3n Input buffer 4 Address recorder 5 Latch circuit

Claims (1)

[Claims] 1. A plurality of insulating circuits to which an input circuit through which a current flows when an external contact closes, and outputting digital signals depending on the presence or absence of the current; and a plurality of insulating circuits that output digital signals according to the presence or absence of the current; an address recorder that sequentially controls a plurality of input buffers that receive the digital signals from the insulating circuit and transmit them to the data bus in order to send them to the data bus sequentially; A digital input isolation circuit comprising a latch circuit that latches only the input circuit of the isolation circuit related to the starting input buffer and cuts off the input circuits of other isolation circuits.