Each I/O line is designed with an embedded pullup resistor and an embedded pulldown resistor. The pullup resistor can be enabled or disabled by writing to the Pull-Up Enable Register (PIO_PUER) or Pull-Up Disable Register (PIO_PUDR), respectively. Writing to these registers results in setting or clearing the corresponding bit in the Pull-Up Status Register (PIO_PUSR). Reading a one in PIO_PUSR means the pullup is disabled and reading a zero means the pullup is enabled. The pulldown resistor can be enabled or disabled by writing the Pull-Down Enable Register (PIO_PPDER) or the Pull-Down Disable Register (PIO_PPDDR), respectively. Writing in these registers results in setting or clearing the corresponding bit in the Pull-Down Status Register (PIO_PPDSR). Reading a one in PIO_PPDSR means the pullup is disabled and reading a zero means the pulldown is enabled.
Enabling the pulldown resistor while the pullup resistor is still enabled is not possible. In this case, the write of PIO_PPDER for the relevant I/O line is discarded. Likewise, enabling the pullup resistor while the pulldown resistor is still enabled is not possible. In this case, the write of PIO_PUER for the relevant I/O line is discarded.
Control of the pullup resistor is possible regardless of the configuration of the I/O line.
After reset, depending on the I/O, pullup or pulldown can be set.