All peripherals on a device, with the exception of infrastructure peripherals such as
SYSCTL itself and the IOMUX, require two user actions to enable the peripheral to be
ready for operation:
- Peripheral Write Enable
- Provided by the peripheral write enable control register (PWREN)
with a KEY and ENABLE field.
- Before any other peripheral registers are configured by software,
the peripheral itself must be enabled by writing the ENABLE bit
together with the appropriate KEY value to the peripheral's PWREN
register
- When the PWREN.ENABLE bit is cleared, the peripheral's registers are
not accessible for read/write operations.
- Peripheral Function Enable
- Peripherals may have a functional enable bit in the corresponding
register map to provide access to power or for operation
Note: After setting the ENABLE | KEY bits in the PWREN
register to enable a peripheral, wait at least 4 ULPCLK clock cycles before
accessing the rest of the peripheral's memory-mapped registers. The 4 cycles
allow for the bus isolation signals at the peripheral's bus interface to
update.