27.5.4.4 I/O Line State Retention in Hibernate and Backup Modes

When entering Hibernate or Backup mode, PORTs are powered off but the pin configuration is retained. When the device exits the Hibernate or Backup mode, the I/O line configuration can either be released or stretched, based on the I/O Retention bit in the CTRLA register (CTRLA.IORET).

If IORET = 0 when exiting Hibernate or Backup mode, the I/O lines configuration is released and driven by the reset values of each PORT.

If the IORET = 1 when exiting Hibernate or Backup mode, the configuration of the I/O lines is retained until the IORET bit is written to 0. It allows the I/O lines to be retained until the application has reprogrammed each PORT.