Electronic Control Apparatus With Defined Reset Function

The present invention relates to electronic control apparatus, and more particularly to electronic control apparatus which operates in accordance with predetermined clock signals, such as microprocessors; and especially to such apparatus suitable for use in installations in which operation of the microprocessors is frequently interrupted at random times, for example microprocessors installed in automotive vehicles.

Various types of electrical apparatus, such as microprocessors, memory systems and arrays, computation circuits, and the like, operate in accordance with fixed clock signals. It is well known that such apparatus should be reset to a predetermined state after interruption of supply voltage. In order to reset the electronic apparatus, it has previously been proposed to generate a short, usually sharp voltage pulse upon energization of the apparatus, which is used as a reset pulse to reset the apparatus to the defined predetermined state. It has been found that such resetting will not, however, necessarily have the desired effect since a clock generator which, frequently, is powered by the same source as the microprocessor, will have not have started full oscillation at the time the reset pulse is received in the remainder of the apparatus. It is thus possible that undefined, stray or interference pulses which might arise upon starting might interfere with the operation of the system, by simulating clock pulses, or being processed in the form of clock pulses. Such stray pulses would, then, cause operation of the electronic apparatus so that, when the actual clock pulses start, the state of the apparatus will not be as thought, that is, in the predetermined defined state, but rather in the random state as determined by such extraneous or stray pulses. Thus, voltage-dependent resetting of electronic control apparatus is often not sufficient to reset the apparatus to the predetermined state. The problem is particularly acute in connection with automotive-type microprocessor control systems due to the frequent and random interruption of power supply thereto. Upon removal of all electrical power from the vehicle, for example upon opening of a main switch, or removal of the battery, operation of the microprocessor is terminated; likewise, the clock signal generator which furnishes predetermined clock signals is shut down. Restarting of the clock signal, as well as the microprocessor, will occur at random times, as determined and desired by the operator of the vehicle. It is important that the microprocessor start operation from a predetermined state in order to properly process sensed signals derived from engine sensors, for example.

It is an object to so control operation of electronic control apparatus, and especially microprocessors and associated apparatus, particularly when used in an automotive environment where random and frequent interruption or shutdown and restarting may occur, and in which operation of the microprocessor, as programmed, is insured.

Briefly, a system is provided to insure oscillation of the clock generator, providing clock pulses before the microprocessor itself is enabled upon resumption of processing operation, for example after shutdown or interruption of power supply thereto. In accordance with a feature of the invention, a rectifier is provided connected to the clock generator and rectifying the output thereof. The rectified output is connected to the reset input of the electrical apparatus, typically the microprocessor, so that only when the clock generator provides a defined predetermined output sufficient to stably operate, the microprocessor itself will be enabled. The circuit connection to the microprocessor to start it after reset may include logic gates which require both a starting pulse to start the microprocessor and sufficient clock signal output which, upon concurrence of both, then reset the microprocessor for subsequent processing operations under control of the then available clock signals.

The system has the advantage that the microprocessor will be reset only when the clock generator already is fully oscillating. This, then, insures that one of the essential control signals utilized by the circuit of the control system is reliably present after the reset terminal has been energized. The system has the further advantage that the microprocessor will be reset to start new computations or new processing sequences or cycles each time that clock pulses should fail, for example upon momentary or short-time failure of operation of the clock generator, or upon masking of clock signals, for example by stray noise signals which may arise in automotive vehicles, for example when the vehicle passes beneath or adjacent to a high-tension power line, a railroad catenary system, or another installation which may induce stray signals of sufficient strength to mask operating signals within a processing system.

In accordance with a preferred feature of the invention, the reset signal derived from the clock generator is logically joined with a voltage-dependent or otherwise generated external reset pulse. This arrangement permits resetting of the microprocessor and other electronic equipment either manually or in conjunction with operating conditions, e.g. (a) proper oscillation of the clock generator, and (b) presence of adequate supply voltage. The microprocessor will then operate only if both conditions are satisfied.

In accordance with a preferred feature of the invention, the reset circuit and/or the clock generator is at least, in part, integrated with the microprocessor, thereby reducing external accessory circuits used in connection therewith.

The single FIGURE is a schematic block diagram of the system of the present invention.

A clock generator 1 has its output 1 a connected to the clock input terminal 7b of a microprocessor 7. The output of the clock generator 1 further is connected to a diode 2 and a resistor 3 in series therewith. Resistor 3 is connected to an input 6a of a logic circuit 6. Positive supply voltage applied from terminal 4a is connected through a diode 4 to the input terminal 6a of the logic circuit 6. The input terminal 6a of the logic circuit is, additionally, connected to ground or chassis through an R/C circuit 9, 5. The logic circuit 6 has an additional input 8 to which an external reset pulse can be connected. The output of the logic circuit 6 is connected to the reset input 7a of the microprocessor 7. The external reset pulse to terminal 8 can be derived, for example, from a differentiating circuit connected to the operating control switch for the microprocessor 7 so that, when the operating control switch is energized, a pulse will be available at terminal 8. The length of the pulse can be suitably timed.

Operation: Let it be assumed that the microprocessor 7 should operate. The logic circuit 6 and the clock generator 1 will be supplied with external operating power, for example derived from a power source P. The logic circuit 6 is so arranged that its output will have a signal appear thereon which retains the microprocessor 7 in reset condition. When the generator 1 is oscillating fully, a clock signal will be available at its output terminal 1a which is rectified by the peak rectifier formed by diode 2 and resistor 3 as well as capacitor 5. Diode 2 rectifies the output from clock generator 1 and, when the value of the rectified output signal is sufficiently high, it will be suitable for energization of the logic circuit 6. Resistor 9 is a pull-down resistor which prevents undesired charge accumulation on the logic circuit 6. Diode 4 permits rapid discharge of capacitor 5 upon disconnection of operating power from terminal P. A logic 1-signal at the output of the peak rectifier 2, 3, 5 then provides cancellation of the reset signal being applied to the input terminal 7a of the microprocessor 7.

The logic circuit 6 is not strictly necessary. It can be eliminated if the reset input 7a of the microprocessor 7 should be switched only based on clock pulses from the clock pulse generator 1. In accordance with circuit selection and requirements, the logic circuit 6 can be formed as an AND-gate, an OR-gate, a NAND-gate, or as a NOR-gate; alternatively, it can be formed as a flip-flop. If the reset pulse should only be cancelled when a concurrence of conditions occurs: (a) suitable oscillation of the clock generator 1, and (b) adequate operating voltage suitable for microprocessor operation, then the logic circuit 6 should be formed, depending on the internal circuit structure of the microprocessor 7, either as an AND-gate or as a NAND-gate. The reset cycle is terminated then only when: (a) the clock generator 1 oscillates properly, and (b) the voltage-dependent reset signal is available on terminal 8. Manual resetting can be achieved by means of a manually operable switch connected, for example, to terminal 8. Under such conditions, the logic circuit 6 preferably is selected to be an OR-gate or a NOR-gate. The microprocessor then can be reset either upon manual operation of the switch (not shown) or upon failure of clock signals from the clock generator 1.

The number of the reset inputs applied to the logic circuit 6, that is, the types of reset signals applied to terminal 8, for example through an OR-gate, can be extended as required; the logic interconnection of these additional signals will be determined by the particular wiring and logic structure of the microprocessor 7 as well as by the desired number of signals and their characteristics.

The clock signals from clock generator 1, after the microprocessor has been reset, are applied from the output terminal 1a to the clock input 7b of the microprocessor.

The entire circuit arrangement, including the reset control terminal 7a, and the other circuit components can be integrated with the microprocessor chip. This, then, reduces the number of externally required structural elements.

The system is not limited to use with microprocessors, but can be used with any type of electrical control apparatus which functions in accordance with recurring clock signals, such as various types of computation apparatus, storage and memory circuits, and the like, as well as digitally operating control systems.