Atmel SAM4L Xplained Pro Starter Kit Atmel ATSAM4L-XSTK ATSAM4L-XSTK Data Sheet

42023E–SAM–07/2013

When a GPIO pin is assigned to a peripheral function, i.e. the corresponding bit in GPER is zero,
output and output enable is controlled by the selected peripheral pin. In addition the peripheral
may control some or all of the other GPIO pin functions listed in 

, if the peripheral sup-

ports those features. All pin features not controlled by the selected peripheral is controlled by the
GPIO.

Refer to the Module Configuration section for details regarding implemented GPIO pin functions
and to the Peripheral chapter for details regarding I/O pin function control.

Pull-up and pull-down can be configured for each GPIO pin. Pull-up allows the pin and any con-
nected net to be pulled up to VDD if the net is not driven. Pull-down pulls the net to GND. 

Pull-up and pull-down are useful for detecting if a pin is unconnected or if a mechanical button is
pressed, for various communication protocols and to keep unconnected pins from floating.

Pull-up can be enabled and disabled by writing a one and a zero respectively to the correspond-
ing bit in the Pull-up Enable Register (PUER). Pull-down can be enabled and disabled by writing
a one and a zero respectively to the corresponding bit in the Pull-down Enable Register (PDER). 

 shows the timing of the GPIO pin when writing to the Output Value Register (OVR).

The same timing applies when performing a ‘set’ or ‘clear’ access, i.e. writing to OVRS or
OVRC. The timing of PVR is also shown.

I/O Pin function Control

Output

OVR

Peripheral

Output enable

ODER

Peripheral

Pull-up

PUER

Peripheral if supported, else GPIO

Pull-down

PDER

Peripheral if supported, else GPIO

Drive strength

ODCRn

Peripheral if supported, else GPIO

Slew rate

OSRRn

Peripheral if supported, else GPIO

Schmitt trigger

STER

Peripheral if supported, else GPIO