JPH03158915A - Power supply voltage drop detector - Google Patents

Abstract

PURPOSE:To exactly detect the drop of a power supply voltage in accordance with the actual characteristic of each device even when the characteristics of respective devices for constituting a microcomputer are different from each other by providing a delaying circuit on the prescribed data path of the microcomputer. CONSTITUTION:Such a prescribed processing as data passes through a data path into which a delaying circuit 13 is inserted is executed. That is, since the delay quantity of the delaying circuit 13 increases in accordance with the drop of a power supply voltage, the drop of the power supply voltage can be detected by discriminating whether the time required for the prescribed processing is within a prescribed time or not. In this case, the delay quantity is increased by reflecting the actual lowest operating voltage of each device. In such a manner, the drop of the power supply voltage can be detected exactly in accordance with each characteristic even when the characteristics of respective devices are different from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply voltage drop detection device for a microcomputer.

[Prior Art] In a one-chip microcomputer having a central processing unit (CPL), a storage device, and a peripheral processing device, the system is often driven by a battery or the like. In such a case, a situation may occur in which the power supply voltage becomes lower than the minimum operating voltage of the system. In order to prevent malfunction of the system due to such a drop in power supply voltage, a microcomputer is provided with a power supply voltage drop detection device.

A generally known conventional power supply voltage drop detection device of this type is a device that compares the output of a constant voltage generation circuit with the power supply voltage and detects whether the power supply voltage has fallen below the minimum operating voltage of the system. .

[Problems to be Solved by the Invention] However, the conventional power supply voltage drop detection device as described above has the following disadvantages.

In general, the minimum operating voltages of individual devices constituting a microcomputer differ within a certain range depending on variations in characteristics of each device. For this reason, in a conventional power supply voltage drop detection device that compares a constant voltage with a power supply voltage, it is necessary to set the constant voltage, which is a criterion, to be equal to or higher than the maximum value of the variation in the minimum operating voltage of each device. However, with such a configuration, there is a risk that the system may actually be fully operational even though the power supply voltage drop detection device has determined that the system is inoperable.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power supply voltage drop detection device that can accurately detect a drop in power supply voltage even when the characteristics of individual devices constituting a microcomputer are different from each other.

[Means for Solving the Problems] The features of the present invention that achieve the above-mentioned objects include a delay circuit inserted into a predetermined data path of a microcomputer, and means for executing a predetermined process in which data passes through this data path. and a means for determining whether the time required for the above-mentioned predetermined processing by the execution means is within a predetermined time.

[Action] Execute a predetermined process such that data passes through the data path in which the delay circuit is inserted. Since the amount of delay of the delay circuit increases as the power supply voltage decreases, a decrease in the power supply voltage can be detected by determining whether the time required for a predetermined process is within a predetermined time. In this case, the amount of delay increases to reflect the actual minimum operating voltage of the individual device. Therefore, even if the characteristics of individual devices differ from each other, it is possible to accurately detect a drop in the power supply voltage according to the characteristics of each device.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram schematically showing the configuration of an embodiment of the present invention, and FIG. 2 is a flowchart showing a part of a voltage determination processing program in the embodiment of FIG.

In this embodiment, a delay circuit is provided in the data path within the CPU of a microcomputer. In Figure 1,
10 is an arithmetic circuit in the CPU of the microcomputer; 1
1 is a control circuit for the arithmetic circuit 10, 12 is a latch that stores the result of the arithmetic operation, and 13 is a delay circuit provided in the data path 14 between the arithmetic circuit 1G and the latch 12.

The microcomputer executes the voltage determination processing program shown in FIG. 2 at regular intervals or before and after predetermined processing. First, in step S1, the arithmetic circuit IO is instructed to perform a predetermined arithmetic operation and store it in the latch 12. Next, in step S2, the contents of the latch 12 are read. In the next step S3, it is determined whether the read content is the correct result of the above-mentioned predetermined calculation. “
YES”, that is, if the result is correct, step S
Proceed to step 4 and output a signal indicating that the power supply voltage is normal.

If the result is "No", that is, if the result is not correct, the process advances to step S5, and a signal indicating that the power supply voltage is decreasing is output.

Since each of the above-mentioned steps is executed every cycle of the system clock, a certain period of time will elapse from the start of arithmetic processing in step S1 until the reading in step S2. If correct calculation results cannot be obtained after this certain period of time has elapsed, the delay circuit 1
In this case, it is determined that the delay amount of No. 3 has increased.

FIG. 3 is a block diagram schematically showing the configuration of another embodiment of the present invention, and FIG. 4 is a flowchart showing a part of the voltage determination processing program in the embodiment of FIG.

In this embodiment, a delay circuit is provided in the carry output path of the arithmetic circuit in the CPU of the microcomputer.

In Figure 3, 20 is the 8-bit A that holds the arithmetic number.
Register 21 is an 8-bit B register that holds the operand, and 22 is an arithmetic circuit (ALU) that performs the addition operation in this case.
), 23 is an 8-bit R register that holds the calculation result, 24 is a flag register that holds the carry output of the calculation result, and 25 is a delay provided in the carry output path 26 between the calculation circuit 22 and the flag register 24. Each circuit is shown.

The microcomputer executes the voltage determination processing program shown in FIG. 4 at regular intervals or before and after predetermined processing. First, in step Sll, data A is set in the A register 20, and in step St2, data B is set in the B register 21. Next step S13
Now, the arithmetic circuit 22 is instructed to perform the arithmetic operation of A+B. In step 514, the contents of the flag register 24 are checked to determine whether the carry output is correctly set to "1". If "YES", that is, if the result is correct, the process advances to step S15 and a signal indicating that the power supply voltage is normal is output. If "No", that is, if the result is not correct, the process advances to step S16, and a signal indicating that the power supply voltage has decreased is output.

Since each of the above steps is executed every cycle of the system clock, a certain period of time will elapse from the start of calculation in step S13 until the carry output is determined in step SI4.

If a correct carry output is not obtained after the predetermined period of time has elapsed, it is determined that the delay amount of the delay circuit 25 has increased due to a drop in the power supply voltage. In addition,
It is assumed that the above-mentioned A+B operation is such that the carry output becomes "1". For example, if A+H is performed when A=FF and B=1, the result will be R=00 and carry output C=1. Particularly, this calculation is advantageous because the processing time is maximized and the amount of delay can be easily identified.

FIG. 5 is a block diagram schematically showing the configuration of still another embodiment of the present invention, and FIG. 6 is a flowchart showing a part of the voltage determination processing program in the embodiment of FIG.

In this embodiment, a delay circuit is provided in a data path between a CPU of a microcomputer and a peripheral processing unit. In FIG. 5, 30 is the CP of the microcomputer.
U, 31 is a peripheral processing device, and 32 is a delay circuit provided in a data path 33 between the CPU 30 and the peripheral processing device 31.

The microcomputer executes the voltage determination processing program shown in FIG. 6 at fixed time intervals or before and after predetermined processing. First, in step 521, the peripheral processing device 3I
instructs to transfer data to Then step S
At 22, data is read from the peripheral processing device 31. In the next step S23, it is determined whether the read data matches the data transferred to the peripheral processing device 31. If "YES", that is, if correct transfer has been performed, the process advances to step S24 and a signal indicating that the power supply voltage is normal is output. If "No", that is, if the correct transfer has not been performed, the process advances to step 325, and a signal indicating that the power supply voltage has decreased is output.

Each of the above steps is also executed every cycle of the system clock, so a certain amount of time will elapse from the start of transfer in step 321 until the readout in step 322, and the correct transfer result will not be obtained after this certain period of time has elapsed. If this is not possible, the delay circuit 3
It is determined that the amount of delay of No. 2 has increased.

Although the present invention has been described using the above three embodiments, it is clear that the delay circuit of the present invention may be inserted at any position in the pig path of a microcomputer.

[Effects of the Invention] As described above, the power supply voltage drop detection device of the present invention includes: a delay circuit inserted into a predetermined data path of a microcomputer; a means for executing a predetermined process in which data passes through the data path; Since the execution means is equipped with a means for determining whether or not the time required for the above-mentioned predetermined processing is within the predetermined time period, a drop in the power supply voltage can be detected even if the characteristics of the individual devices constituting the microcomputer are different from each other. However, it has the special effect of being able to accurately detect each device according to its actual characteristics, and that this detection can be performed with a simple circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing the configuration of an embodiment of the present invention, FIG. 2 is a flowchart showing a part of the voltage determination processing program in the embodiment of FIG. 1, and FIG. FIG. 4 is a flow chart showing a part of the voltage determination processing program in the embodiment of FIG. 3, and FIG. 5 is a block diagram schematically showing the configuration of another embodiment of the present invention. FIG. 6 is a flowchart showing a part of the voltage determination processing program in the embodiment of FIG. 5. l0122... Arithmetic circuit, 11... Control circuit, 12... Latch, 13.25.32.
...Delay circuit, 14.33...Data path, 20. 21. 23...Register, 24...Flag register, 26...Canon output path, 30...CPU. 31... Peripheral processing device. Shikakein (504) Nyabu (1 type company 1 JP-A-3 158915 (5)

Claims (1)

[Claims] A delay circuit inserted into a predetermined data path of a microcomputer, a means for executing a predetermined process in which data passes through the data path, and whether the time required for the predetermined process by the execution means is within a predetermined time. A power supply voltage drop detection device comprising: means for determining.