The GPIO mux registers must be configured to connect this peripheral to the device pins. To avoid glitches on the pins, the GPyGMUX bits must be configured first (while keeping the corresponding GPyMUX bits at the default of zero), followed by writing the GPyMUX register to the desired value.
For proper SDFM operation, use the following GPIO input qualification. Other GPIO qualifications are not supported.
- GPIO Input qualification is ASYNC, make sure to check the SDFM Electrical Data and Timing (Using ASYNC) requirement is met and be aware of the following caution message. SDFM Input Qualification feature is used to provide protection against random noise glitches.
- Recommended option: GPIO Input qualification = 3-sample GPIO
Input Qualification. This option provides additional hardware protection
against occasional random noise glitches. When GPIO Input qualification is a
3-sample window, make sure to check that the SDFM Electrical Data and Timing
(Using 3-Sample GPIO Input Qualification) requirement is met and be aware of
the following caution message and note.
CAUTION: The SDFM clock
inputs (SDx_Cy pins) directly clock the SDFM module. Any glitches or ringing noise
on these inputs can corrupt the SDFM module operation. Special precautions must be
taken on these signals to make sure of a clean and noise-free signal that meets SDFM
timing requirements. Precautions such as series termination for ringing due to any
impedance mismatch of the clock driver and spacing of traces from other noisy
signals are recommended.
Note: The SDFM module expects SD-Dx to
change on the falling edge of SD-Cx and strobes for SD-Dx on the rising edge. But
some SD-modulators in the market change SD-Dx on the rising edge and expect SDFM to
strobe for data on the falling edge. In such cases, the GPIO inversion feature
(GPxINV) is used on SD-Cx pin to change polarity and make it compatible with the
SDFM.
The SDFM Qualified GPIO (3-sample) option provides protection against SDFM
module corruption due to occasional random noise glitches on the SDx_Cy pin that
can result in a false comparator trip and filter output.
The SDFM Qualified GPIO (3-sample) option does not provide protection against
persistent violations of the above timing requirements. Timing violations
results in data corruption proportional to the number of bits that violate the
requirements.
See the General-Purpose Input/Output (GPIO) chapter for more details on GPIO mux and settings.