Ensuring that
a microcontroller runs only during valid environmental condition is usually
critically important to an application. It is very apparent that reset can only
take place when you are sure power to the microcontroller is valid.
a microcontroller runs only during valid environmental condition is usually
critically important to an application. It is very apparent that reset can only
take place when you are sure power to the microcontroller is valid.
Typically, microcontroller application begin to
operate when power is applied to the device. To ensure that power has stabilized,
using the circuit shown below in fig. 2.2 below. With this circuit, reset
become actively approximately 22ms (using the approximation of the time delay =
2.2RC) after power comes up. This gives a lot of time for power and the devices
oscillator to stabilize before the microcontroller begins operation.
operate when power is applied to the device. To ensure that power has stabilized,
using the circuit shown below in fig. 2.2 below. With this circuit, reset
become actively approximately 22ms (using the approximation of the time delay =
2.2RC) after power comes up. This gives a lot of time for power and the devices
oscillator to stabilize before the microcontroller begins operation.
The “momentary
on push button” (manual reset) is used to allow resetting the application
during application development. When you are debugging an application, you will
find that it is useful to control reset and be able to restart the
microcontroller. The 100ohm resistor in series with the capacitor will limit
current from the capacitor during reset (a charge capacitor will behave like a high
current source when shorted to ground). This circuit can be used with
microcontrollers, which have a positive active reset (such as the 80510) by
inverting the voltage at the capacitor (using a 7404).
on push button” (manual reset) is used to allow resetting the application
during application development. When you are debugging an application, you will
find that it is useful to control reset and be able to restart the
microcontroller. The 100ohm resistor in series with the capacitor will limit
current from the capacitor during reset (a charge capacitor will behave like a high
current source when shorted to ground). This circuit can be used with
microcontrollers, which have a positive active reset (such as the 80510) by
inverting the voltage at the capacitor (using a 7404).
The reset
circuit is best used in applications where the power voltage (Vcc) can be
guaranteed to be within operating limits. Many microcontroller application rely
on batteries, which produce lower voltage over time. As the voltage drops, this
may make the application run erratically, as some devices cut-off voltage is
reached before others.
circuit is best used in applications where the power voltage (Vcc) can be
guaranteed to be within operating limits. Many microcontroller application rely
on batteries, which produce lower voltage over time. As the voltage drops, this
may make the application run erratically, as some devices cut-off voltage is
reached before others.
To eliminate
this as a problem, there are devices known as “blownout” circuit design to
monitor the Vcc level, and if it drops below a predetermined point ( usually
4.5 volts), reset will be asserted actively. Typically, these
voltage-monitoring circuits include a delay to operate similarly to the RC
reset circuit shown in fg. 2.2 above and monitor the incoming voltage level and
are packed similarly to a three-leaded transistor.
this as a problem, there are devices known as “blownout” circuit design to
monitor the Vcc level, and if it drops below a predetermined point ( usually
4.5 volts), reset will be asserted actively. Typically, these
voltage-monitoring circuits include a delay to operate similarly to the RC
reset circuit shown in fg. 2.2 above and monitor the incoming voltage level and
are packed similarly to a three-leaded transistor.
