LM3S2965-IQC20-A0T Luminary Micro, Inc., LM3S2965-IQC20-A0T Datasheet - Page 460

• Manufacturer Part Number: LM3S2965-IQC20-A0T
• Description: Microcontroller
• Manufacturer: Luminary Micro, Inc.

Pulse Width Modulator (PWM)
18.2.3
460
Figure 18-3. PWM Count-Up/Down Mode
CompA
CompB
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 18-4 on page 460 shows the use of Count-Up/Down mode to generate a pair of
center-aligned, overlapped PWM signals that have different duty cycles.
Figure 18-4. PWM Generation Example In Count-Up/Down Mode
CompA
CompB
PWMA
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
PWMB
Load
Load
Load
Zero
Zero
Zero
Dir
A
B
BUp
AUp
ADown
BDown
Preliminary
June 04, 2007