19.6.3.4 I/O Lines Retention in BACKUP Mode

When entering BACKUP mode, the PORT is powered off but the pin configuration is retained. When the device exits the 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 BACKUP mode, the I/O lines configuration is released and driven by the reset value of the PORT.
• If the IORET=1 when exiting 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 programmed the PORT.