The GTB functionality is implemented by the GTBEEN and GTBEOUT bits in the
CONF register, the input signal gtb_in, and the output signal gtb_out. The GTBEEN bit
enables gtb_in to control the FTM counter enable signal:
• If GTBEEN = 0, each one of FTM modules works independently according to their
configured mode.
• If GTBEEN = 1, the FTM counter update is enabled only when gtb_in is 1.
In the configuration described in the preceding figure, FTM modules A and B have their
FTM counters enabled if at least one of the gtb_out signals from one of the FTM modules
is 1. There are several possible configurations for the interconnection of the gtb_in and
gtb_out signals, represented by the example glue logic shown in the figure. Note that
these configurations are chip-dependent and implemented outside of the FTM modules.
See the chip-specific FTM information for the chip's specific implementation.
NOTE
• In order to use the GTB signals to synchronize the FTM
counter of different FTM modules, the configuration of
each FTM module should guarantee that its FTM counter
starts counting as soon as the gtb_in signal is 1.
• The GTB feature does not provide continuous
synchronization of FTM counters, meaning that the FTM
counters may lose synchronization during FTM operation.
The GTB feature only allows the FTM counters to start
their operation synchronously.
39.4.28.1
Enabling the global time base (GTB)
To enable the GTB feature, follow these steps for each participating FTM module:
1. Stop the FTM counter: Write 00b to SC[CLKS].
2. Program the FTM to the intended configuration. The FTM counter mode needs to be
consistent across all participating modules.
3. Write 1 to CONF[GTBEEN] and write 0 to CONF[GTBEOUT] at the same time.
4. Select the intended FTM counter clock source in SC[CLKS]. The clock source needs
to be consistent across all participating modules.
5. Reset the FTM counter: Write any value to the CNT register.
To initiate the GTB feature in the configuration described in the preceding figure, write 1
to CONF[GTBEOUT] in the FTM module used as the time base.
Chapter 39 FlexTimer Module (FTM)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 1023
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