NXP Semiconductors KE1xF Series, Reference Manual, Page: 1175 / 1483

44.5.3.4 Glitch filter bypassed
In Pulse Counter mode, when the glitch filter is bypassed, the selected input source
increments the CNR every time it asserts. Before the LPTMR is first enabled, the selected
input source is forced to be asserted. This prevents the CNR from incrementing if the
selected input source is already asserted when the LPTMR is first enabled.
44.5.4 LPTMR compare
When the CNR equals the value of the CMR and increments, the following events occur:
• CSR[TCF] is set.
• LPTMR interrupt is generated if CSR[TIE] is also set.
• LPTMR hardware trigger is generated.
• CNR is reset if CSR[TFC] is clear.
When the LPTMR is enabled, the CMR can be altered only when CSR[TCF] is set. When
updating the CMR, the CMR must be written and CSR[TCF] must be cleared before the
LPTMR counter has incremented past the new LPTMR compare value.
44.5.5 LPTMR counter
The CNR increments by one on every:
• Prescaler clock in Time Counter mode with prescaler bypassed
• Prescaler output in Time Counter mode with prescaler enabled
• Input source assertion in Pulse Counter mode with glitch filter bypassed
• Glitch filter output in Pulse Counter mode with glitch filter enabled
The CNR is reset when the LPTMR is disabled or if the counter register overflows. If
CSR[TFC] is cleared, then the CNR is also reset whenever CSR[TCF] is set.
When the core is halted in Debug mode:
• If configured for Pulse Counter mode, the CNR continues incrementing.
• If configured for Time Counter mode, the CNR stops incrementing.
The CNR cannot be initialized, but can be read at any time. On each read of the CNR,
software must first write to the CNR with any value. This will synchronize and register
the current value of the CNR into a temporary register. The contents of the temporary
register are returned on each read of the CNR.
When reading the CNR, the bus clock must be at least two times faster than the rate at
which the LPTMR counter is incrementing, otherwise incorrect data may be returned.
Chapter 44 Low Power Timer (LPTMR)
Kinetis KE1xF Sub-Family Reference Manual, Rev. 4, 06/2019
NXP Semiconductors 1175