LM3S6110 Luminary Micro, Inc, LM3S6110 Datasheet - Page 374

• Manufacturer Part Number: LM3S6110
• Description: Lm3s6110 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Pulse Width Modulator (PWM)
15.2
15.2.1
15.2.2
374
Figure 15-2. PWM Module Block Diagram
PWM Clock
Functional Description
PWM Timer
The timer runs in one of two modes: Count-Down mode or Count-Up/Down mode. In Count-Down
mode, the timer counts from the load value to zero, goes back to the load value, and continues
counting down. In Count-Up/Down mode, the timer counts from zero up to the load value, back
down to zero, back up to the load value, and so on. Generally, Count-Down mode is used for
generating left- or right-aligned PWM signals, while the Count-Up/Down mode is used for generating
center-aligned PWM signals.
The timers output three signals that are used in the PWM generation process: the direction signal
(this is always Low in Count-Down mode, but alternates between Low and High in Count-Up/Down
mode), a single-clock-cycle-width High pulse when the counter is zero, and a single-clock-cycle-width
High pulse when the counter is equal to the load value. Note that in Count-Down mode, the zero
pulse is immediately followed by the load pulse.
PWM Comparators
There are two comparators in the PWM generator that monitor the value of the counter; when either
match the counter, they output a single-clock-cycle-width High pulse. When in Count-Up/Down
mode, these comparators match both when counting up and when counting down; they are therefore
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 15-3 on page 375 shows the behavior of the counter and the relationship of these pulses
when the counter is in Count-Down mode. Figure 15-4 on page 375 shows the behavior of the counter
and the relationship of these pulses when the counter is in Count-Up/Down mode.
Interrupts /
Triggers
PWM Generator Block
PWMnCOUNT
PWMnLOAD
PWMnCMPA
PWMnCMPB
PWMnCTL
zero
load
dir
cmp A
cmp B
Preliminary
Interrupt and
PWMnINTEN
PWMnGENA
PWMnGENB
Generator
PWMnRIS
PWMnISC
Trigger
PWMnMINFLTPER
PWMnFLTSTAT0
PWMnFLTSRC0
PWMnFLTSEN
PWMnDBRISE
PWMnDBFALL
PWMnDBCTL
July 25, 2008
PWMn_Fault
PWMn_A
PWMn_B
Fault(s)