mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 767

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

In pulse counter mode with the prescaler/glitch filter bypassed, the selected input source
directly clocks the LPTMR counter register 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.
35.4.3 LPTMR prescaler/glitch filter
The LPTMR prescaler and glitch filter share the same logic which operates as a prescaler
in time counter mode and as a glitch filter in pulse counter mode.
The prescaler/glitch filter configuration must not be altered when the LPTMR is enabled.
35.4.3.1 Prescaler enabled
In time counter mode when the prescaler is enabled, the output of the prescaler directly
clocks the LPTMR counter register. When the LPTMR is enabled, the LPTMR counter
register will increment every 2
enabled, the first increment of the LPTMR counter register will take an additional one or
two prescaler clock cycles due to synchronization logic.
35.4.3.2 Prescaler bypassed
In time counter mode when the prescaler is bypassed, the selected prescaler clock
increments the LPTMR counter register on every clock cycle. When the LPTMR is
enabled, the first increment will take an additional one or two prescaler clock cycles due
to synchronization logic.
35.4.3.3 Glitch filter
In pulse counter mode when the glitch filter is enabled, the output of the glitch filter
directly clocks the LPTMR counter register. When the LPTMR is first enabled, the
output of the glitch filter is asserted (logic one for active high and logic zero for active
low). If the selected input source remains negated for at least 2
prescaler clock rising edges, then the glitch filter output will also negate. If the selected
Freescale Semiconductor, Inc.
The clock source selected may need to be configured to remain
enabled in low power modes, otherwise the LPTMR will not
operate during low power modes.
MCF51JF128 Reference Manual, Rev. 2, 03/2011
2
to 2
16
prescaler clock cycles. After the LPTMR is
Preliminary
NOTE
Chapter 35 Low Power Timer (LPTMR)
1
to 2
15
consecutive
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