Data Sheet

1011
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181G–SAM-D21_Datasheet–09/2015
38.4 External Reset Circuit
The external reset circuit is connected to the RESET pin when the external reset function is used. If the external reset
function has been disabled, the circuit is not necessary. The reset switch can also be removed, if the manual reset is not
necessary. The RESET
pin itself has an internal pull-up resistor, hence it is optional to also add an external pull-up
resistor.
Figure 38-4. External Reset Circuit Example Schematic
A pull-up resistor makes sure that the reset does not go low unintended causing a device reset. An additional resistor has
been added in series with the switch to safely discharge the filtering capacitor, i.e. preventing a current surge when
shorting the filtering capacitor which again causes a noise spike that can have a negative effect on the system.
Notes: 1. These values are given as a typical example.
2. The SAM D21 features an internal pull-up resistor on the RESET
pin, hence an external pull-up is optional.
38.5 Unused or Unconnected Pins
For unused pins the default state of the pins for the will give the lowest current leakage. There is thus no need to do any
configuration of the unused pins in order to lower the power consumption.
Table 38-3. Reset Circuit Connections
Signal Name Recommended Pin Connection Description
RESET
Reset low level threshold voltage
V
DDIO
= 1.6V - 2.0V: Below 0.33 * V
DDIO
V
DDIO
= 2.7V - 3.6V: Below 0.36 * V
DDIO
Decoupling/filter capacitor 100nF
(1)
Pull-up resistor 10kΩ
(1)(2)
Resistor in series with the switch 330Ω
(1)
Reset pin
GND
RESET
100nF
10kΩ
V
DD
330Ω