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.