DE4409286C1 - Method detecting cause of reset in microprocessor controlled system - Google Patents

Abstract

The method involves recognising from the voltage at the microprocessor port immediately after reset if it is a short or long reset. A reset operation is caused either by switch-on of an external supply voltage (long-reset) or by short term fluctuations of the supply voltage and also by failure states (short-reset). A capacitor (16) is charged when an external supply voltage is present. The capacitor discharges with a predetermined discharge time constant, which is longer than the short reset, when there is a faulty external supply voltage. The capacitor is connected to a port (12) of the microprocessor which is connected as an input port directly after a reset so that the microprocessor can direct from the presence of a voltage on the port after a reset state whether the reset is short or long.

Description

The invention relates to a method for recognizing the causes of a reset Operation of a system controlled by a microprocessor according to the Preamble of the main claim. The invention further relates to a circuit for Carrying out the method according to the preamble of claim 2.

From GB 22 43468 A is an IC card with a microprocessor, one Data input circuit and a data output circuit known. Next are one Reset receiving device for receiving an external reset signal and a Monitoring timer provided, the monitoring timer being an internal Reset signal generated when a predetermined period of time has elapsed within the the data input circuit receives no external response. The Reset receiving device and the monitoring timer are over one Discriminator circuit connected to the microprocessor, which Discriminator circuit decides whether there is an external or internal reset signal and, depending on this, triggers further command sequences.

WO 89/09957 describes a microcomputer with a device for Distinguish reset signals. An OR gate is provided, at the there is a cyclic reset signal at one input and the other input with a Reset output of a power supply unit is connected. The output of the gate is connected to the reset input of the microprocessor. To between cyclical Reset signals and reset signals coming from the power supply unit To be able to distinguish is the reset output of the power supply unit additionally via a memory element with a further input of the microprocessor connected, which is queried by the microprocessor when a reset signal occurs becomes. In this way it is possible to reset the cyclic reset signals from the Differentiate power supply unit coming from reset signals.

When a system controlled by a microprocessor is switched on generally a "supply voltage on reset" or a "power on reset" generated to all in an initialization phase of the system or the microprocessor Registers, memory, I / O ports (input / output connections) etc. in to configure in a predetermined manner. Can while the system is operating  due to drops in the supply voltage, for example as a result of Interference voltages, or also due to error states determined by the software Resets are triggered that reconfigure the system.

In practice, it is often desirable to be able to distinguish whether a Reset by deliberately switching the system off and then on again (long-term reset) or due to error conditions during operation, such as voltage fluctuations and / or Error states detected by the software (the Voltage fluctuations) (short-term reset) was caused.

For example, information of sizes stored in a buffered Memory after "supply voltage off" until the next operating cycle should be saved, falsified by a reset generated by faults or are displayed incorrectly and therefore make no sense, so that after a "fault reset" the data in the buffered memory (RAM or E²PROM) is deleted or deleted Neutral values are replaced. In the case of a regular "Power On" reset, the stored data validity. An example is the storage of sensor / actuator Diagnostic errors by monitoring plausibility limits, which are characterized by Interference voltages can erroneously result and thus lead to an unwanted Make an incorrect entry in the diagnostic memory.

The invention has for its object to a method and a circuit indicate its implementation, with which the causes of a reset in simple Way can be determined.  

The part of the object of the invention relating to the method is included in the Features of the main claim solved.

The part of the invention task related to the circuit is with the Features of claim 2 solved.

The subclaims relate to advantageous embodiments of the circuits according to the invention directed.

The invention is described below with the aid of schematic drawings for example and explained in more detail.

They represent:

Fig. 1 shows a first embodiment of a circuit for recognizing the causes of a reset process and

Fig. 2 shows a second embodiment of a circuit.

According to Fig. 1 2 comprises a voltage-supply unit includes a switch 4 and is connected to a supply voltage input 6 and a reset input 8 of a microprocessor 10 is connected, which, for example, the ignition and injection controls an internal combustion engine in known manner, an unillustrated system.

The microprocessor 10 has a connection which can be switched both as an input and as an output, an I / O port 12 which is connected to a capacitor 16 via a charging resistor 14 . A discharge resistor 18 is connected in parallel with the capacitor 16 .

The function of the circuit described is as follows:
After switching on the switch 4 , after the initialization phase of the microprocessor 10, its I / O port 12 is switched as an output, whereupon the capacitor 16 is charged via the charging resistor 14 . After the system has been switched off by opening the switch 4 , the capacitor 16 discharges via the discharge resistor 18 , the resistance of which is chosen to be greater than that of the charging resistor 14 . The discharge time constant τ = R × C (R: size of the discharge resistor 18 , C: capacitance of the capacitor 16 ) is selected so that it is significantly longer than a reset phase caused by disturbances in the supply voltage or by errors detected by the software.

If the system is now switched off regularly via the switch 4 , the capacitor 16 discharges via the discharge resistor 18 . If the system is then put into operation via the switch 4 , the microprocessor 10 recognizes, due to the lack of a voltage on the I / O port 12 which was initially connected as an input after the reset phase, that this reset is a "regular" Long-term reset acted. The I / O port is then switched as an output again, so that the capacitor 16 is charged.

If a brief reset state occurs during operation, for example as a result of a voltage dip or as a result of an error detected by the software, the microprocessor 10 detects by the voltage at the I / O port 12 connected as input (the capacitor is 16) not yet discharged) that it was a "short-term reset". The I / O port is then switched as an output again, so that the capacitor 16 is fully charged again.

With the information obtained after a reset phase about the Past before the reset or its reasons, different, Actions controlled by the system software are performed.

In this embodiment of the circuit, the capacitor 16 is always discharged via the discharge resistor 18 . The port 12 is used to charge the RC element 16 , 18 and to measure the voltage of the capacitor 16 after a reset.

Fig. 2 shows a modified embodiment of the circuit, for which various modifications are conceivable. According to Fig. 2 of the charging resistor 14 is of the capacitor 16 is connected directly to the power supply unit 2. The port 20 of the microprocessor 10 , to which the capacitor 16 is connected via a connection resistor 22 , is basically connected as an input port. The port 20 can also be an A / D connection of the microprocessor 10 , via which analog voltages can be detected.

Claims (6)

1. A method for detecting the causes of a reset process of a system controlled by a microprocessor ( 10 ), a reset process either by switching on an external supply voltage (long-term reset) or by brief fluctuations in the external supply voltage and also by the Software of the microprocessor ascertained error states (short-term reset) is triggered, characterized in that, when an external supply voltage is present, a capacitor ( 16 ) is charged which, in the absence of an external supply voltage, discharges with a predetermined discharge time constant which is longer than the duration of a short-term reset and that the capacitor ( 16 ) is connected to a port ( 12 ; 20 ) of the microprocessor ( 10 ) which is connected at least immediately after a reset as an input port, so that from the presence of a voltage at the port immediately after a reset state is recognizable by the microprocessor whether an abbreviation eit reset or a long-term reset was present. 2. Circuit for performing the method according to claim 1 with a switch ( 4 ) for switching on / off a supply voltage unit ( 2 ) for supplying power to a microprocessor ( 10 ), characterized by a capacitor ( 16 ) which has a charging resistor ( 14 ) connected to the supply voltage unit ( 2 ) and connected in parallel to a discharge resistor ( 18 ), the pole of the capacitor ( 16 ) connected to the supply voltage unit ( 2 ) via the charging resistor ( 14 ) being connected as an input port at least immediately after a reset state Port ( 12 ; 20 ) of the microprocessor ( 10 ) is connected. 3. A circuit according to claim 2, characterized in that the port of the microprocessor ( 10 ) is an input / output port ( 12 ) on which the charging resistor ( 14 ) of the capacitor ( 10 ) is located. 4. A circuit according to claim 2, characterized in that the charging resistor ( 14 ) of the capacitor ( 10 ) is connected directly to the supply voltage unit ( 2 ). 5. A circuit according to claim 4, characterized in that the port of the microprocessor ( 10 ) is an analog / digital input ( 20 ). 6. Circuit according to one of claims 2 to 5, characterized in that the voltage supply unit ( 2 ) controls a reset input ( 8 ) of the microprocessor ( 10 ).