Information

37.4.3.3 Glitch filter
In Pulse Counter mode, when the glitch filter is enabled, the output of the glitch filter
directly clocks the CNR. When the LPTMR is first enabled, the output of the glitch filter
is asserted, that is, logic 1 for active-high and logic 0 for active-low. The following table
shows the change in glitch filter output with the selected input source.
If Then
The selected input source remains deasserted for at least 2
1
to 2
15
consecutive prescaler clock rising edges
The glitch filter output will also deassert.
The selected input source remains asserted for at least 2
1
to
2
15
consecutive prescaler clock rising-edges
The glitch filter output will also assert.
NOTE
The input is only sampled on the rising clock edge.
The CNR will increment each time the glitch filter output asserts. In Pulse Counter mode,
the maximum rate at which the CNR can increment is once every 2
2
to 2
16
prescaler
clock edges. When first enabled, the glitch filter will wait an additional one or two
prescaler clock edges due to synchronization logic.
37.4.3.4 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.
37.4.4 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.
Chapter 37 Low-Power Timer (LPTMR)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 837