Microcontroller power-up delay

• US 5,454,114 A
• Filed: 04/04/1994
• Issued: 09/26/1995
• Est. Priority Date: 11/12/1991
• Status: Expired due to Fees

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Mitra, Sumit, Yach, Randy L.
• Primary Examiner(s): Davis, George B.
• Application Number:
  US08/238,121
• Time in Patent Office: 540 Days
• Field of Search: 395/750, 395/550, 364/200, 364/900, 364/493, 364/511, 364/431.11, 364/707, 731/9.1
• US Class Current: 713/330
• CPC Class Codes: G06F 1/24 Resetting means
• CPC Class Codes: G06F 11/221 to test buses, lines or interfaces, e.g. stuck-at or open line faults

Abstract

A microcontroller is adapted, when operating, to execute programs and instructions and, in response, to generate control signals to selectively control external apparatus. The microcontroller includes a power supply for supplying power to the overall device within a predetermined range suitable for its operation, and a clock for supplying a clock frequency to the microcontroller with a stability suitable for precise timing and counting within the device. The microcontroller is selectively reset to prevent it from executing programs and instructions for purposes of generating the control signals, and is maintained in the reset condition despite initiation of a removal from the reset condition, until the power supplied by the power supply is in a predetermined range and the clock frequency supplied by the clock is stable. In this way, no execution by the microcontroller is permitted until device stability is achieved, to prevent errors in execution. In the disclosed embodiment, the reset condition is maintained by a power-up timer and an oscillator start-up timer, each timer having a programmable timeout interval to end the reset condition only when the timeout intervals of both timers have expired.

Claims

1. A microcontroller having a normal operating mode for execution of programs and instructions to generate control signals for selectively controlling external apparatus, said microcontroller comprising:

a power supply for powering the microcontroller in an operating power range having predetermined lower and upper limits, for enabling microcontroller operation in said normal operating mode;

clock means for generating a stable clock frequency to enable said microcontroller to perform precise timing and counting functions when in said normal operating mode; and

reset circuit means for disabling the normal operating mode to render the microcontroller incapable of executing programs and instructions whenever said power supply is operating outside said predetermined limits, said reset circuit means for resetting the microcontroller to operate in the normal operating mode when said clock means is stable;

said reset circuit means including a power-up timer and a clock means start-up timer, each said timer having a separately programmable time-out interval to initiate a reset of the microcontroller to the normal operating mode only when the time-out intervals of both timers have elapsed.

2. The microcontroller of claim 1, in which:

said reset circuit means further includes means for terminating a programmed time-out interval of the power-up timer if power is restored to said operating power range before said programmed time-out interval of the power-up timer has elapsed.

3. A microcontroller having a normal operating mode for execution of programs and instructions to generate control signals for selectively controlling external apparatus, said microcontroller comprising:

a power supply for powering the microcontroller to enable microcontroller operation in said normal operating mode;

clock means for generating a clock frequency to enable microcontroller performance of precise timing and counting functions when in said normal operating mode; and

reset circuit means for disabling the normal operating mode to render the microcontroller incapable of executing programs and instructions whenever power to said microcontroller falls below a predetermined limit, said reset circuit means for resetting microcontroller operation to the normal operating mode when said clock means is stable and when power to the microcontroller is above said predetermined limit;

said reset circuit means including a power-up timer and a clock means start-up timer, each said timer having a separately programmable time-out interval related, for the power-up timer, to a time interval required for power to stabilize after being restored to a level above said predetermined limit, and for the clock start-up timer, to a time interval required for the clock frequency to stabilize following power restoration, whereby to initiate a reset of the microcontroller to the normal operating mode only when both the clock frequency and the power have stabilized.

4. The microcontroller of claim 3, in which:

said reset circuit means further includes means for terminating a programmed time-out interval of the power-up timer if power is stabilized before said programmed time-out interval of the power-up timer has elapsed.

5. A method for assisting error-free execution of programs and instructions by a microcontroller in a normal operating mode, to enable the microcontroller to generate control signals for selectively controlling external apparatus, said method comprising the steps of:

powering the microcontroller to a power level above a predetermined minimum level to enable microcontroller operation in said normal operating mode;

generating a clock frequency to enable microcontroller performance of precise timing and counting functions when in said normal operating mode;

disabling the normal operating mode to render the microcontroller incapable of executing programs and instructions whenever power to said microcontroller falls below said predetermined minimum level, and

resetting microcontroller operation to the normal operating mode when said clock frequency has stabilized after restoration of power above said predetermined minimum level,

further including programming separate first and second time intervals to commence, respectively, with restoration of power and with re-initiation of clock frequency generation, for the power and the re-initiated clock frequency to stabilize, whereby to return the microcontroller to the normal operating mode when the programmed first and second time intervals have elapsed.

6. The method of claim 5, further including the step of:

ending the programmed first time interval prematurely when the power level is above said predetermined minimum level.