One conventional approach to resetting a microcontroller requires external or internal precision devices to provide a reset into a particular power-on mode. Another conventional approach uses internal timers to keep a microcontroller in the reset condition for a fixed amount of time after a low-voltage condition occurs. Both of theses approaches attempt to bring the microcontroller into a known running condition after the reset occurs.
Referring to FIG. 1, a circuit 10 illustrating a conventional approach for resetting a microcontroller is shown. The circuit 10 generally includes a power supply 12 and an integrated circuit 14. The integrated circuit 14 includes a low voltage detector 16, a hold-off timer 18 and a microcontroller 20. The low voltage detector 16 has an input 22 that receives a voltage from the power supply 12. The low voltage detector 16 responds to a voltage at the input 22 exceeding a predetermined threshold by presenting a signal at an output 24. The signal at the output 24 is presented to an input 26 of the hold-off timer 18 as well as to an input 28 (i.e., a Reset input) of the microcontroller 20. The hold-off timer 18 presents a signal (i.e., Operate) at an output 30 that is presented at an input 32 (i.e., a Run input) of the microcontroller 20. With such a configuration, the low voltage detector 16 is implemented as a precision voltage detector that may be either internal or external to the integrated circuit 14. A precision voltage detector may be required to determine when the voltage at the power supply 12 reaches a level sufficient for the proper operation of the integrated circuit 14.
The main disadvantage with the circuit 10 is that it is difficult to reset the microcontroller 20 into a known running condition while the voltage at the power supply 12 is low. It may also be difficult to keep the microcontroller 20 properly operating in a known condition while the voltage received at the power supply 12 continues to transition to the final and specified operating range after exceeding the predetermined turn on voltage. As a result, the microcontroller 20 must be able to operate at a sufficiently low voltage to allow the reset circuitry (i.e., the low voltage detector 16 and the hold-off timer 18) to operate properly. To provide proper functioning of the microcontroller 20, the hold-off timer 18 may be required to present a hold-off time that may be incompatible (i.e., too long) with overall system power-up/response time requirements.