LM3S5P36 Datasheet, PDF (874/1050 Pages) Texas Instruments – Stellaris® LM3S5P36 Microcontroller

Pulse Width Modulator (PWM)
19.3.2
PWM Comparators
Each PWM generator has two comparators that monitor the value of the counter; when either
comparator matches the counter, they output a single-clock-cycle-width High pulse, labelled "cmpA"
and "cmpB" in the figures in this chapter. When in Count-Up/Down mode, these comparators match
both when counting up and when counting down, and thus are qualified by the counter direction
signal. These qualified pulses are used in the PWM generation process. If either comparator match
value is greater than the counter load value, then that comparator never outputs a High pulse.
Figure 19-3 on page 874 shows the behavior of the counter and the relationship of these pulses
when the counter is in Count-Down mode. Figure 19-4 on page 875 shows the behavior of the counter
and the relationship of these pulses when the counter is in Count-Up/Down mode. In these figures,
the following definitions apply:
■ LOAD is the value in the PWMnLOAD register
■ COMPA is the value in the PWMnCMPA register
■ COMPB is the value in the PWMnCMPB register
■ 0 is the value zero
■ load is the internal signal that has a single-clock-cycle-width High pulse when the counter is
equal to the load value
■ zero is the internal signal that has a single-clock-cycle-width High pulse when the counter is zero
■ cmpA is the internal signal that has a single-clock-cycle-width High pulse when the counter is
equal to COMPA
■ cmpB is the internal signal that has a single-clock-cycle-width High pulse when the counter is
equal to COMPB
■ dir is the internal signal that indicates the count direction
Figure 19-3. PWM Count-Down Mode
LOAD
COMPA
COMPB
0
load
zero
cmpA
cmpB
dir
BDown
ADown
874
January 21, 2012
Texas Instruments-Production Data