NXP Semiconductors K22F series, Reference Manual, Page: 739 / 1407

If the auto-acknowledge feature is disabled (CSCR[AA] is 0) for an address that
generates an error, then the transfer can be terminated by asserting FB_TA. If the
processor must manage a bus error differently, then asserting an interrupt to the core
along with FB_TA when the bus error occurs can invoke an interrupt handler.
The device can hang if FlexBus is configured for external termination and the CSPMCR
is not configured for FB_TA.
31.5 Initialization/Application Information
31.5.1 Initializing a chip-select
Before using any other chip select to take it out of global chip select mode, you must
initialize CS0.
To initialize a chip-select:
1. Write to the associated CSAR.
2. Write to the associated CSCR.
3. Write to the associated CSMR, including writing 1b to the Valid field (CSMRn[V]).
31.5.2 Reconfiguring a chip-select
To reconfigure a previously-used chip-select:
1. Invalidate the chip-select by writing 0b to the associated CSMR's Valid field
(CSMRn[V]).
2. Write to the associated CSAR.
3. Write to the associated CSCR.
4. Write to the associated CSMR, including writing 1b to the Valid field (CSMRn[V]).
Chapter 31 External Bus Interface (FlexBus)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 739