JP2637849B2 - Microcomputer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcomputer having a circuit for handling analog signals.

[0002]

2. Description of the Related Art A circuit for handling analog signals in a conventional microcomputer (hereinafter referred to as an analog circuit), for example, one having a built-in AD converter or DA converter, has a central processing circuit (hereinafter referred to as a CPU) such as an arithmetic circuit and a timing generation circuit. ) And the analog circuit were operated by the same power supply. In the CPU, since processing is performed using digital signals, a signal has two values, a high potential (hereinafter, referred to as a _VDD potential) and a low potential (hereinafter, referred to as a GND potential).
The potential difference between the values is the power supply voltage. Now, the operation of the inverter (see FIG. 3) and the power supply voltage will be described as an example of the CPU. When V _DD potential is applied to input 10, PchMO
The S transistor 12 (hereinafter, referred to as PchMOS) is turned off, the NchMOS transistor 13 (hereinafter, referred to as NchMOS) is turned on, and the GND potential is output to the output. At this time, in order for the NchMOS 13 to be turned on, the difference between the gate voltage and the source voltage, that is, the difference between the input potential ( _VDD potential) and the GND potential must be higher than the threshold voltage of the NchMOS13. On the other hand, when the GND potential is applied to the input, the Nch MOS 13 is turned off, the Pch MOS 12 is turned on, and the _VDD potential is output at the output. At this time, in order for the Pch MOS 12 to be turned on, the difference between the gate voltage and the source voltage, that is, the difference between the input potential (GND potential) and the _VDD potential is PchM.
It must be higher than the threshold voltage of OS12. As described above, in order for the CPU to operate, the difference between the _VDD potential and the GND potential, that is, the power supply voltage is equal to the NchMOS 13 and the PchMO.
It is understood that it is only necessary to be higher than the threshold voltage of S12.

Next, the operation power supply voltage of the analog circuit will be described. As an example of the analog circuit, the AD shown in FIG.
The converter will be described. When the comparison signal 16 is at the low level, the switch element 19 is turned on to short-circuit the points B and C, so that both the NchMOS 21 and the PchMOS 20 are turned on, and the voltages at the points B and C are NchMOS21 and PchM
The voltage is divided by the on-state resistance of OS20. After that, the comparison signal 16 becomes high level, and the switching element 19
There was off, the switch element 18 off and then the control signal 14 is changed from low to high the switch element 17 from ON is turned on from off, instead off voltage of the point A V _in is the V _VEF, B point Changes with the potential change of the point A through the capacitor 22. This fluctuation is compared with NchMOS21 and PchM
The signal is amplified by the OS 20 and output to the point C. For such an operation, when the comparison signal 16 is low, the potential at the point B is Nch
It must be a divided voltage of the on-resistance of the MOS21 and the PchMOS20. For that purpose, NchMOS21 and PchMOS20
Must be turned on, the potential difference between _VDD and the point B must be equal to or greater than the threshold voltage of the PchMOS 20, and the potential difference between the point B and GND must be equal to or greater than the threshold voltage of the NchMOS 21. That is, the power supply voltage needs to be equal to or higher than the sum of the threshold voltages of the PchMOS 20 and the NchMOS 21.

As described above, the analog circuit has a lower CP.
A higher power supply voltage is required for operation than U.

[0005]

In a conventional microcomputer, the minimum operating voltage of an analog circuit is higher than that of a CPU. The circuit operates abnormally, and the CPU operates normally.
If the analog circuit operates abnormally, the output signal of the analog circuit becomes erroneous data. In the calculation of the average value, etc., a plurality of data of the output signal of the erroneous data are stored and processed. There were drawbacks including:

SUMMARY OF THE INVENTION An object of the present invention is to provide a microcomputer which eliminates such disadvantages and which can avoid erroneous processing of a device due to erroneous data in an analog signal processing circuit.

[0007]

SUMMARY OF THE INVENTION The present invention has a minimum operating voltage that is higher than the minimum operating voltage of a digital signal processing circuit in a device connected to the device power supply where voltage fluctuations occur. In a microcomputer provided with an analog signal processing circuit for giving a processing result of its own circuit to a digital signal processing circuit, a voltage of the device power supply is detected, and when the detected voltage falls below a minimum operating voltage of the analog signal processing circuit, the digital signal is output. A power supply voltage detection circuit for providing a prohibition signal for prohibiting the signal processing circuit from capturing the processing result of the analog signal processing circuit; the digital signal processing circuit responding to the prohibition signal to generate a processing result of the analog signal processing circuit; It is characterized in that it includes means for temporarily stopping the capturing.

The means for calculating the average of the processing results of the analog signal processing circuit included in the digital signal processing circuit includes:
It is desirable that the means be a means for executing an averaging operation excluding the processing result of the analog signal processing circuit whose capture has been suspended.

[0009]

When the device power supply voltage drops to an intermediate value between the minimum operating voltage of the digital signal processing circuit and the minimum operating voltage of the analog signal processing circuit, the digital signal processing circuit performs normal processing. The result is incorrect. The digital signal processing circuit temporarily stops taking in the erroneous processing result to avoid the erroneous processing.

[0010]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of this embodiment. The power supply voltage detection circuit 1 changes the power supply voltage detection signal 5 from a high level to a low level when detecting a voltage lower than a certain voltage difference between _VDD and GND. The voltage to be detected is set to the minimum operating power supply voltage of the analog circuit 2. The analog circuit 2 is an analog / digital conversion circuit that converts the analog input signal 4 into a digital signal 6. The central processing circuit 3 takes in the digital signal 6 and controls the set by a program.

That is, as shown in FIG. 1, this embodiment is connected to an apparatus power supply in which voltage fluctuations occur, and is controlled by a minimum operating voltage of a CPU 3 which is a digital signal processing circuit in the apparatus connected to the apparatus power supply. An analog circuit 2 having a high minimum operating voltage and providing the digital signal processing circuit with the processing result of its own circuit is provided. Further, as a feature of the present invention, the voltage of the device power supply is detected and A power supply voltage detection circuit for providing a prohibition signal for prohibiting the CPU from capturing the processing result of the analog circuit when the voltage falls below the minimum operating voltage of the circuit; Means for temporarily stopping the acquisition of the processing result of the circuit 2 is included. The averaging means for the processing results of the analog circuit 2 included in the digital signal processing circuit is means for executing the averaging operation excluding the processing results of the analog circuit 2 whose capture has been suspended.

Next, the operation of this embodiment will be described. When a voltage equal to or higher than the detection voltage set in the power supply voltage detection circuit 1 is applied between the high potential terminal and the low potential terminal, a high level is output as the power supply voltage detection signal 5.
When a high level is output to the power supply voltage detection signal 5, CP
U3 performs processing using the data of the digital signal 6.
When the power supply voltage decreases, for example, when the life of the battery is shortened using a battery as a power supply, and the potential difference between the high potential terminal and the low potential terminal becomes equal to or less than the detection voltage of the power supply voltage detection circuit 1, that is, equal to or less than the minimum operation power supply voltage of the analog circuit 2, The analog circuit 2 outputs data having an error in the digital signal 6, and the power supply voltage detection circuit 1 outputs a low level to the power supply voltage detection signal 5.

As an example, the output of the temperature sensor is converted into a digital signal by an AD converter which is an analog circuit 2,
The CPU 3 constitutes a device which takes in and stores temperature data which is the output of the AD converter at regular time intervals, calculates an average value based on the stored data, and performs temperature control. C
The PU 3 not only performs arithmetic processing using the data of the analog circuit 2, but also performs processing such as reading setting data from a key and transmitting data to the display circuit. With this configuration, when the power supply voltage detection signal 5 goes low, the CPU
3 receives the power supply voltage detection signal 5 as an interrupt signal and performs an interrupt process. In the interrupt process, a process of reading a key, a process of sending data to a display circuit, and the like are performed, and a process is performed without capturing output data of an AD converter. As a result, data with errors is not stored, so when the power supply voltage is increased and the output data of the analog circuit becomes normal,
The calculation of the average value can be performed immediately using the stored data having no error.

[0015]

As described above, according to the present invention, the minimum operating power supply voltage of the analog circuit is detected by the power supply voltage detection circuit, and the central processing circuit detects the analog circuit having an error by the signal detected by the power supply voltage detection circuit. Since the processing is performed without taking in the output signal, the processing can be performed without storing erroneous data, and there is an effect that an error does not occur in the processing using the data stored for calculating the average value.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a configuration of a conventional example.

FIG. 3 is a circuit diagram of an inverter as an internal example of a central processing circuit.

FIG. 4 is a circuit diagram of an AD converter as an internal example of an analog circuit.

[Explanation of symbols]

 1 Power supply voltage detection circuit 2 Analog circuit 3 Central processing circuit 4 Analog input signal 5 Power supply voltage detection signal 6 Digital signal 10 Input 11 Output 12, 20 PchMOS transistor 13, 21 NchMOS transistor 14 Control signal 15 Reference voltage signal 16 Comparison signal 17, 18, 19 switch element

Claims (2)

(57) [Claims] 1. An apparatus connected to a device power supply in which voltage fluctuation occurs.
A microcomputer provided with an analog signal processing circuit having a minimum operating voltage higher than a minimum operating voltage of a digital signal processing circuit in a device connected to the device power supply, and providing the digital signal processing circuit with a processing result of its own circuit. A power supply voltage for detecting a voltage of the power supply of the device and supplying a prohibition signal for prohibiting the digital signal processing circuit from taking in the processing result of the analog signal processing circuit when the detected voltage is lower than the minimum operating voltage of the analog signal processing circuit. A microcomputer comprising a detection circuit, wherein the digital signal processing circuit includes means for temporarily stopping taking in of the processing result of the analog signal processing circuit in response to the prohibition signal. 2. The averaging means of the processing result of the analog signal processing circuit included in the digital signal processing circuit is means for executing an averaging operation excluding the processing result of the analog signal processing circuit whose capture has been suspended. The microcomputer according to 1.