JP2000113362A - Two-wire signal transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow the operation of a transmitter to have allowance, and to increase the degree of freedom of circuit design by decreasing the frequencies of the operating clock of an arithmetic control part only at the time of writing data in a non-volatile memory. SOLUTION: A frequency dividing means 131 generates a frequency division clock from the generated clock of a clock generator 126 in an arithmetic control part 130. This frequency division clock is used as the operating clock of the arithmetic control part 130. A frequency rate controlling means 132 controls the frequency rate of a frequency dividing means 131. A writing controlling means 133 transmits a control signal to the frequency division controlling means 132 for changing a frequency division rate and for decreasing the frequencies of the frequency division clock at the time of writing data in a non-volatile memory 125. Then, the writing controlling means 133 monitors a signal transmitted from a transmission line, and writes data in a non-volatile memory 125 at the time of detecting that communication data are superimposed on an electric signal transmitted from the transmission line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-wire signal transmitter for converting a physical quantity measured by a sensor into an electric signal and transmitting the electric signal to a load via two transmission lines. . More specifically, the present invention relates to a device for reducing current consumption when writing data in a nonvolatile memory inside a transmitter.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a configuration example of a conventional two-wire signal. In FIG. 3, the two-wire signal transmitter 10 includes:
The electric signal is transmitted to the load via the two transmission lines 31 and 32. On the load side, for example, there is a distributor 40. The distributor 40 performs A / D conversion (analog / digital conversion) on the transmitted electric signal and passes it to a computer (not shown). The communication terminal 50 is connected to the transmission line and communicates with the two-wire signal transmitter 10.

A two-wire signal transmitter 10 includes an input circuit 11 for receiving a measurement input of a sensor and an output circuit 12 for converting the received measurement input into an electric signal of a predetermined format and transmitting the signal to a transmission line. Become. In the input side circuit 11, the multiplexer 111 selects one of the measurement inputs S1, S2, S3 of the sensor. The A / D converter 112 converts the measurement input selected by the multiplexer 111 into digital data. The photocoupler PC1 insulates and transmits the converted digital data to the output side circuit 12. DC / DC converter CO
N is the power of the power supply in the output side circuit 12
Feed to 1. The power supply voltage is taken from the line L1.

In the output circuit 12, an arithmetic control unit 121 reads digital data transmitted by the photocoupler PC1, performs necessary arithmetic operations, and sends the arithmetic result to the output current control unit 122 as output data. Output current control unit 122
Controls the transistor Q1 to convert output data into an electric signal of a predetermined format, for example, a current signal of 4 to 20 mA, and sends it to the transmission lines 31 and 32 via the terminals 123 and 124. Operation control unit 121 and output current control unit 122
Is composed of, for example, a microcomputer.

The operation control unit 121 includes an output current control unit 122
The communication terminal 50 communicates with the communication terminal 50 by superimposing communication data on an output (a current signal of 4 to 20 mA) by a communication interface circuit (not shown) incorporated in the communication terminal 50. Non-volatile memory 12
The operation control unit 121 is connected to the communication terminal 5.
From 0, data such as an operation mode and a correction coefficient can be written. The operation mode includes, for example, types of sensors such as thermocouples and resistance temperature detectors. As the correction coefficient,
For example, there are coefficients used when performing calibration. As the nonvolatile memory 125, for example, an EEPROM is used.

The clock generator 126 has an arithmetic control unit 121
Generates a clock that is the basis of the operation clock of The arithmetic control unit 121 divides the frequency of the clock generated by the clock generator 126 and uses the divided clock as the operation clock.

In the two-wire signal transmitter shown in FIG. 3, for example, the temperature measured by a temperature sensor is set to 0 to 100.degree.
It shall correspond to 0 mA. When the measurement temperature is 0 ° C., the maximum current consumption of the transmitter is 4 mA, and the transmitter must operate at a current of about 3.2 mA to provide a margin. However, since a nonvolatile memory such as an EEPROM consumes a large amount of current at the time of writing, it may exceed the allowable current consumption of the transmitter of 4 mA at the time of writing. Although the maximum current consumption can be suppressed by lowering the frequency of the operation clock of the arithmetic control unit 121, there is a problem that the response of the output to the input becomes slow.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problem. The present invention has been made to reduce the frequency of an operation clock of an arithmetic control unit only at the time of writing to a non-volatile memory. Allow time for operation,
An object of the present invention is to realize a two-wire signal transmitter that can increase the degree of freedom in circuit design.

[0009]

SUMMARY OF THE INVENTION The present invention is a two-wire signal transmitter having the following configuration.

(1) In a two-wire signal transmitter for converting a physical quantity measured by a sensor into an electric signal and transmitting the electric signal to a load side via two transmission lines, the electric signal is superimposed on the electric signal on the transmission line. A non-volatile memory into which the communication data is written, an A / D converter for converting the measurement signal of the sensor from analog to digital, and reading the conversion data from the A / D converter to perform a predetermined operation. An operation control unit that sends out as output data and controls writing to the nonvolatile memory, and an output signal control unit that converts the output data into an electric signal of a predetermined format and sends out the transmission signal to a transmission line. The two-wire signal transmitter, wherein the arithmetic control unit lowers the frequency of its own operation clock when writing data to the nonvolatile memory.

(2) The arithmetic control unit includes frequency dividing means for generating a frequency-divided clock serving as an operation clock from a clock generated by a clock generator, and frequency dividing ratio controlling means for controlling a frequency dividing ratio of the frequency dividing means. And writing control means for sending a control signal to the frequency division ratio control means when writing to the non-volatile memory to change the frequency division ratio and lower the frequency of the frequency division clock. The two-wire signal transmitter according to 1).

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention. 1 that are the same as those in FIG. 3 are given the same reference numerals. This embodiment shows a case where the DC / DC converter is a self-excited DC / DC converter.

The arithmetic and control unit 130 includes the nonvolatile memory 12
When writing data to 5, the frequency of its own operation clock is lowered. The configuration for this will be described.

In the arithmetic control unit 130, the frequency dividing means 131 generates a frequency-divided clock from the clock generated by the clock generator 126. This frequency-divided clock becomes the operation clock of the arithmetic control unit 130. The dividing ratio control means 132
The division ratio of 1 is controlled. When writing to the non-volatile memory 125, the write control unit 133 sends a control signal to the division ratio control unit 132 to change the division ratio and lower the frequency of the divided clock.

The write control means 133 monitors a signal sent from the transmission line, and the communication data is superimposed on an electric signal (a current signal of 4 to 20 mA in the embodiment) sent from the transmission line. When this is detected, data is written to the nonvolatile memory 125.

FIG. 2 is a signal time chart of the write operation. As shown in FIG. 2, the arithmetic control unit 130 in which the clock frequency division ratio is variable allows the nonvolatile memory 125
The frequency of the operation clock is reduced only when writing to the memory. For example, 2 MHz during normal operation and 1 MHz during writing
The frequency of the operation clock is switched such as MHz.

When the frequency of the operation clock is reduced,
The response of the output to the input is somewhat slower, but the accuracy of the output is maintained. Further, the frequency of writing to the nonvolatile memory is low, and the time required for writing is short, so that there is almost no practical problem.

[0018]

According to the present invention, the following effects can be obtained.

According to the first and second aspects of the present invention, the following effects can be obtained. When the output is small, the current consumption of the transmitter has a margin,
The degree of freedom in circuit design increases. Output accuracy can be maintained even during writing to the nonvolatile memory.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating the operation of the present invention.

FIG. 3 is a diagram showing a configuration example of a conventional two-wire signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Two-wire signal transmitter 31, 32 Transmission line 122 Output current control part 125 Nonvolatile memory 130 Operation control part 131 Dividing means 132 Dividing ratio control means 133 Writing control means

Claims (2)

[Claims] 1. A two-wire signal transmitter for converting a physical quantity measured by a sensor into an electric signal and transmitting the electric signal to a load via two transmission lines, wherein the electric signal is superimposed on the electric signal on the transmission line. Memory to which the communication data is written, and A / D for converting the measurement signal of the sensor from analog to digital
A converter; a conversion controller that reads conversion data of the A / D converter, performs a predetermined calculation, sends out a calculation result as output data, and controls writing to the nonvolatile memory; And an output signal control unit for converting the signal into an electric signal of a predetermined format and transmitting the signal to a transmission line, wherein the arithmetic control unit lowers the frequency of its own operation clock when writing data to the nonvolatile memory. A two-wire signal transmitter. 2. The frequency controller according to claim 1, wherein the arithmetic control unit generates a frequency-divided clock that is an operation clock from a clock generated by a clock generator; and a frequency-division ratio controller that controls a frequency-division ratio of the frequency-divider. And writing control means for sending a control signal to the frequency division ratio control means to change the frequency division ratio to lower the frequency of the frequency division clock when writing to the non-volatile memory. 2. The two-wire signal transmitter according to 1.