Device-Level Timers
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
21-7
Other count modes derived as special cases of the modes described in Table 21-3 are described
in the remainder of this section.
21.1.4.1
One-Shot Mode
One-Shot mode is a variation on Triggered Count mode if the timer is set up as follows:
TMRxCTL[CM] = 110 to count the rising and falling edges of the primary source
The Count Length bit, TMRxCTL[LEN] = 1.
Output Flag mode, TMRxCTL[OFLM] = 101 to select set on compare, cleared on
secondary input signal edge.
The Count Once bit, TMRxCTL[ONCE] = 1 to count till a compare and then stop.
An external event causes the timer to count. When terminal count is reached, the timer output
flag is asserted. This delayed output assertion can be used to provide timing delays.
21.1.4.2
Pulse Output Mode
In Pulse Output mode, a variation on Count mode, the timer outputs a stream of pulses with the
same frequency as the selected clock source (cannot be the CLASS64 clock/1) if the timer is set
up as follows:
TMRxCTL[CM] = 001 to count the rising edges of the primary source.
(see Table 21-5TMR[0–3]SCTL[0–3] Bit Descriptions, on page 21>-19).
The Output Flag Mode, TMRxCTL[OFLM], = 111 to enable gated clock output while the
timer is active.
The Count Once bit, TMRxCTL[ONCE], = 1 to count till a compare and then stop.
The number of output pulses is equal to the compare value minus the initial value. The primary
count source must be set to one of the timer outputs for gated clock output mode.
21.1.4.3
Fixed Frequency PWM Mode
Fixed Frequency Pulse Width Modulated (PWM) mode is a subset of Count mode. The timer is
set up as follows:
TMRxCTL[CM] = 001 to count the rising edges of the primary source.
The Count Length bit, TMRxCTL[LEN], = 0 so that the timer continues counting past the
compare value (binary roll-over).
The Count Once bit, TMRxCTL[ONCE], = 0 to count repeatedly.
The Output Flag Mode, TMRxCTL[OFLM], = 110 so that the output flag is set when a
compare occurs.
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