Atmel Xplained Pro Evaluation Kit for the ATSAMD21J18A Microcontroller ATSAMD21-XPRO ATSAMD21-XPRO Data Sheet
Product codes
ATSAMD21-XPRO
979
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181C–SAM-D21_Datasheet–07/2014
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.
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.
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
Unused or unconnected pins (unless marked as NC where applicable) should not be left unconnected and floating.
Floating pins will add to the overall power consumption of the device. To prevent this one should always draw the pin
voltage towards a given level, either V
Floating pins will add to the overall power consumption of the device. To prevent this one should always draw the pin
voltage towards a given level, either V
DD
or GND, through a pull up/down resistor. External or internal pull up/down
Table 38-3. Reset Circuit Connections
Signal Name
Recommended Pin Connection
Description
RESET
Reset low level threshold voltage
V
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
Pull-up resistor 10k
Resistor in series with the switch 330
Ω
Reset pin
GND
RESET
100nF
10kΩ
V
DD
330Ω