Hello,
According to section 10.3.2 (SW Loopback through SION bit) of the RT1020 RM:
"A limited option exists to override the default pad functionality and force the input path
to be active (ipp_ibe==1'b1) regardless of the value driven by the corresponding module.
This can be done by setting the SION (Software Input On) bit in the
IOMUXC_SW_MUX_CTL register (when available) to "1".
Uses include:
• LoopBack - Module x drives the pad and also receives pad value as an input."
So, "the software input on (SION) bit is an option to force an input path to be active regardless of the value
driven by the corresponding module. It is used when the nature direction of a pin depending on selected
alternative function is an output, but it is needed to read the real logic value on a pin. [...]
The SION bit can be used in:
• Loopback: the module of a selected alternative function drives the pad and also receives the pad
value as an input;
• GPIO capture: the module of a selected alternative function drives the pin and the value is captured
by the GPIO."
Since I2C data line is bidirectional in its nature, the SION should be set.
Have a nice day.
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