LM3S310 Luminary Micro, Inc, LM3S310 Datasheet - Page 280

• Manufacturer Part Number: LM3S310
• Description: Lm3s310 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Pulse Width Modulator (PWM)
14.2.3
280
Figure 14-3. PWM Count-Up/Down Mode
PWM Signal Generator
The PWM generator takes these pulses (qualified by the direction signal), and generates two
PWM signals. In Count-Down mode, there are four events that can affect the PWM signal: zero,
load, match A down, and match B down. In Count-Up/Down mode, there are six events that can
affect the PWM signal: zero, load, match A down, match A up, match B down, and match B up.
The match A or match B events are ignored when they coincide with the zero or load events. If the
match A and match B events coincide, the first signal, PWMA, is generated based only on the match
A event, and the second signal, PWMB, is generated based only on the match B event.
For each event, the effect on each output PWM signal is programmable: it can be left alone
(ignoring the event), it can be toggled, it can be driven Low, or it can be driven High. These actions
can be used to generate a pair of PWM signals of various positions and duty cycles, which do or
do not overlap. Figure 14-4 shows the use of Count-Up/Down mode to generate a pair of
center-aligned, overlapped PWM signals that have different duty cycles.
Figure 14-4. PWM Generation Example In Count-Up/Down Mode
In this example, the first generator is set to drive High on match A up, drive Low on match A down,
and ignore the other four events. The second generator is set to drive High on match B up, drive
Low on match B down, and ignore the other four events. Changing the value of comparator A
changes the duty cycle of the PWMA signal, and changing the value of comparator B changes the
duty cycle of the PWMB signal.
CompA
CompA
CompB
CompB
PWMA
PWMB
Load
Load
Load
Zero
Zero
Zero
Dir
A
B
BUp
AUp
ADown
Preliminary
BDown
July 5, 2006