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LPTMRx_CNR field descriptions (continued)
Field
Description
COUNTER
Counter Value
The CNR returns the value of the LPTMR counter at the time this register was last written. Writing the
CNR will latch the current value of the LPTMR for subsequent reading, the value written is ignored.
31.5 Functional description
31.5.1 LPTMR power and reset
The LPTMR remains powered in all power modes, including low-leakage modes. If the
LPTMR is not required to remain operating during a low-power mode, then it must be
disabled before entering the mode.
The LPTMR is reset only on global Power On Reset (POR) or Low Voltage Detect
(LVD). When configuring the LPTMR registers, the CSR must be initially written with
the timer disabled, before configuring the PSR and CMR. Then, CSR[TIE] must be set as
the last step in the initialization. This ensures the LPTMR is configured correctly and the
LPTMR counter is reset to zero following a warm reset.
31.5.2 LPTMR clocking
The LPTMR prescaler/glitch filter can be clocked by one of the four clocks. The clock
source must be enabled before the LPTMR is enabled.
NOTE
The clock source selected need to be configured to remain
enabled in low-power modes, otherwise the LPTMR will not
operate during low-power modes.
In Pulse Counter mode with the prescaler/glitch filter bypassed, the selected input source
directly clocks the CNR and no other clock source is required. To minimize power in this
case, configure the prescaler clock source for a clock that is not toggling.
NOTE
The clock source or pulse input source selected for the LPTMR
should not exceed the frequency f
LPTMR
defined in the device
datasheet.
Functional description
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
508
Freescale Semiconductor, Inc.