Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Synchronizing
Reexamination Certificate
1998-12-07
2001-02-13
Wambach, Margaret R. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Synchronizing
C327S143000, C327S160000, C377S002000, C377S016000
Reexamination Certificate
active
06188256
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reset-out circuit, and more particularly, to a micro-controller with a reset-out circuit that allows feeding back the micro-controller reset-out signal to its reset-in input without locking the micro-controller into reset.
2. Discussion of the Prior Art
Micro-controllers typically have a reset state where various circuits of the micro-controllers are initialized prior to commencement of normal operation. For example, the reset state is entered when power is first applied or when certain internal or external conditions occur that cast doubt on continued proper operation of the micro-controllers. Entering the reset state initializes the micro-controller to a known state and allows proper operation thereafter.
A typical micro-controller has a reset-in input pin which receives an external reset signal to reset the micro-controller, e.g., due to a power interrupt. In addition to being reset by the external reset signal, the micro-controller is also reset due to internal conditions. The micro-controller outputs a reset-out signal from a reset-out output pin in response to either the external reset signal received at the reset-in input pin, or an internally generated reset signal. For example, the internal reset signal is generated by a central processing unit (CPU) of the micro-controller in response to execution of a reset instruction, by a timeout of a watchdog timer or by detection of certain error conditions.
It is desirable to use the micro-controller reset-out signal as a single global reset signal provided to all circuits of a device, since the micro-controller reset-out signal is generated in response to either the external or internal reset conditions. When used as a global reset, the micro-controller reset-out signal from the reset-out output pin is fed back to the reset-in input pin of the micro-controller, as well as to other devices in the system.
Feeding back the micro-controller reset-out signal to the micro-controller reset-in input pin presents the potential problem of locking the micro-controller into the reset state permanently. A further problem arises due to the short duration or pulse width of the global system reset signal provided from the micro-controller. A short global system reset signal may not properly reset all devices in a system.
Accordingly, there is a need for a circuit that allows proper operation of a micro-controller in response to both externally and internally generated reset signals where a global system reset output from the micro-controller reset-out output pin is fed back to the micro-controller reset-in input pin without locking the micro-controller in the reset state and causing other problems.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a reset device in a micro-controller, for example, which overcomes the problems of conventional reset devices.
Another object of the present invention is to provide a reset device which distinguishes between an externally-supplied reset and an internally generated one.
A further object of the present invention is to provide a reset device which provides a reset-out pulse of sufficient duration whenever an internally-generated reset is detected.
A still further object of the present invention is to provide a reset device which permits the reset-out pulse from the micro-controller reset-out output pin to be fed-back into the micro-controller reset-in input pin without causing the micro-controller to permanently latch-up.
A yet further object of the present invention is to provide a reset device which permits the user to disable the entire reset-out function of the micro-controller under software control.
Another object of the present invention is to provide a reset device that accomplishes all of the above objects without initializing any of the flip-flops involved during reset or following power-up.
The present invention accomplishes the above and other objects by providing a reset device in a micro-controller, for example. The reset device has a counter which outputs a count enable signal after counting down a predetermined number of counts, for example. An input device of the reset device provides a start signal to the counter for initiating the count-down in response to an input reset signal. An output device outputs an output reset signal in response to the start signal and the count enable signal. The start signal is inhibited by a control signal, which is provided from a control device in response to an external reset signal received at an input pin of the micro-controller.
The input device includes an AND gate which receives the input reset signal. The AND gate also receives an inverted delayed version of the input reset signal and the control signal. The reset device further includes a NOR gate which receives the start signal and the count enable signal to provide the output reset signal. An OR gate receives the outputs from the counter and provides the count enable signal.
REFERENCES:
patent: 4665536 (1987-05-01), Kim
patent: 5228066 (1993-07-01), DeVane
patent: 5521848 (1996-05-01), Bayne et al.
patent: 0679981A2 (1995-11-01), None
patent: WO9724652 (1997-07-01), None
By Motorola, “Intializating Micro-Computer Peripherals” Technical Developments, Motorola Inc. Oct. 1985, vol. 5, pp. 41-43.
Birns Neil Edward
Slivkoff William Jay
Zheng Jie
Philips Electronics North America Corporation
Piotrowski Tony E.
Wambach Margaret R.
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