JPS6234356Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a deadman timer that detects runaway by monitoring the loop processing time of a microcomputer, and in particular to a deadman timer that has a simple configuration yet can reliably monitor the periodic signal that is output in response to the loop processing.

In recent years, with the rapid development of electronic technology, there is a tendency for control by microcomputers to be used in various fields. In this case, when used in automobiles, industrial equipment, etc., the operating conditions are severe, and noise or static electricity may cause the device to run out of control. Therefore, when using a microcomputer, a runaway detection device is used to quickly and reliably detect runaway and switch to fail-safe control.

In this case, the conventionally commonly used runaway detection device is equipped with a deadman timer that monitors the loop processing time, and detects a runaway condition when the period of the periodic signal output in response to the loop processing becomes longer than the set time. It is something to detect.

However, in the dead man timer with the above configuration, the pulse width of the periodic signal is digitally measured by counting the reference clock signal using a counter, so the structure is extremely complicated and expensive. It has the problem of becoming a thing.

Therefore, it is an object of the present invention to provide a dead man timer which has an extremely simple structure and yet provides reliable operation.

In order to achieve this purpose, the present invention provides a charging circuit that charges only during the "H" period of the periodic signal and a charging circuit that charges only during the "L" period of the periodic signal. If either one of the output signals rises above a set value, it is determined that the microcomputer has gone out of control. Hereinafter, the dead man timer according to the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a dead man timer according to the present invention. In the figure, 1 is a microcomputer, and from the output port P _A there is an "H" period with a period T ₀ corresponding to loop processing.
It is configured to generate a periodic signal A of _T1 . Reference numerals 2 and 3 are a resistor and a capacitor connected in series between the power supply +Vcc and the ground, forming a charging circuit. 4 is a discharging transistor connected in parallel between both ends of the capacitor 3 and whose base input is the periodic signal A via a resistor 5; 6 and 7 are a resistor and a capacitor connected in series between the power supply +Vcc and the ground. This makes up the charging circuit. 8 is a discharging transistor 11 connected in parallel between both ends of the capacitor 7 and having the periodic circuit A as a base input via an inverter 9 and a resistor 10;
is a comparator, which uses the outputs of both charging circuits as positive inputs via diodes 12 and 13, and connects the power supply +Vcc.
The upper limit value V _H obtained by dividing the voltage by resistors 14 and 15 is used as the negative input. 16 is “H” of comparator 11
This is an inverter that supplies a reset signal B whose output is inverted to the input port P _B of the microcomputer 1.

In the dead man timer configured in this manner, when a periodic signal A with a duty of 50% is generated from the output port P _A of the microcomputer 1 with a period T ₀ shown in FIG. During this period, the transistor 4 is turned on, and the charge in the capacitor 3 is rapidly discharged. Next, when the periodic signal A becomes "L", the capacitor 3 is charged via the resistor 2 because the transistor 4 is turned off. As a result, the output of the charging circuit constituted by the resistor 2 and the capacitor 3 increases in accordance with the time constant set by the values of the resistor 2 and the capacitor 3, as shown in FIG. 2b. The maximum value increases in accordance with the "L" period width of the periodic signal A. However, during the period of the periodic signal A during normal operation, this integrated output does not reach the set value V _H set by the resistors 14 and 15, and the comparator 11 generates an "L" output. Continue to do so.

Next, if the microcomputer 1 goes out of control for some reason and the period of the periodic signal A becomes longer, the "L" period becomes wider as shown in Figure _2a after time t1. . As a result, the charging output increases in accordance with the "L" period width of the periodic signal A, as shown after time _t1 in FIG. 2b, and exceeds the upper limit value _VH at time _t2 . In this way, when the charging output exceeds the upper limit value _VH , the output of the comparator 11 is inverted and becomes "H", and this "H" output is input to the microcomputer 1 as the reset signal B via the inverter 16. The signal is supplied to port P _B for fail-safe control. In this way,
By monitoring the "L" period for the periodic signal A, the cycle _T0 is monitored and runaway of the microcomputer 1 is detected.

On the other hand, a part of the periodic signal A is inverted in an inverter 9 and then supplied to the base of the transistor 8 via a resistor 10. Therefore, this transistor 8 receives the "L" level of the periodic signal A shown in FIG. 2a.
The capacitor 7 is turned on during the "H" period to quickly discharge the charge on the capacitor 7, and is turned off during the "H" period so that the capacitor 7 is turned on in response to a time constant determined by the values of the resistor 6 and the capacitor 7. It will be charged. As a result, when the "H" period of the periodic signal A becomes longer when the microcomputer 1 runs out of control, the charging output of the charging circuit constituted by the resistor 6 and the capacitor 7 will exceed the upper limit value _VH . At the same time, the output of the comparator 11 is inverted to "H", and the microcomputer 1 is reset.
Therefore, in this case, runaway is detected by monitoring the "H" period of periodic signal A, and as a whole, the "L" period and "H" period of periodic signal A are monitored independently. The microcomputer 1 is monitored to detect abnormalities in the periodic signal A, thereby monitoring runaway of the microcomputer 1.

As explained above, the dead man timer according to the present invention includes a charging circuit that charges the "L" period of the periodic signal output from the microcomputer in response to loop processing, and a charging circuit that charges the "H" period of the periodic signal. When the comparator detects that the output of at least one of these charging circuits exceeds a set level, it determines that the microcomputer is in a runaway state and performs a reset process on the microcomputer. . For this,
Since both the "L" period and the "H" period of the periodic signal are monitored, runaway of the microcomputer can be detected reliably. In addition, without using complicated and expensive digital circuits as in the past,
It has various excellent effects such as being able to detect runaway of a microcomputer with a simple analog circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a dead man timer according to the present invention, and FIGS. 2a and 2b are operation waveform diagrams of various parts of the circuit shown in FIG. 1. 1...Microcomputer, 2, 5, 6, 1
0,14,15...Resistor, 3,7...Capacitor, 4,8...Transistor, 9,16...Inverter, 11...Comparator, 12,13...Diode.

Claims (1)

[Scope of utility model registration request] First and second charging circuits each including a resistor and a capacitor connected in series between a power supply and ground, connected in parallel to the capacitor in the first charging circuit, and connected in a loop from a microcomputer. a first transistor that rapidly discharges a charged charge by being turned on by a periodic signal output in response to processing; an inverter that inverts the periodic signal; and a capacitor in the second charging circuit. a second circuit connected in parallel and turned on by the output signal of the inverter to quickly discharge the charged charge;
When the charging output sent from the first and second charging circuits exceeds a predetermined value, it is determined that the microcomputer is running out of control, and a reset process is applied to the microcomputer. A detstomer timer characterized by being equipped with a container.