LM3S5D91 Datasheet, PDF (1077/1340 Pages) Texas Instruments – Stellaris® LM3S5D91 Microcontroller

Stellaris^® LM3S5D91 Microcontroller
Figure 20-3. PWM Count-Down Mode
LOAD
COMPA
COMPB
0
load
zero
cmpA
cmpB
dir
BDown
ADown
Figure 20-4. PWM Count-Up/Down Mode
LOAD
COMPA
COMPB
0
load
zero
cmpA
cmpB
dir
20.3.3
BUp
AUp
BDown
ADown
PWM Signal Generator
Each PWM generator takes the load, zero, cmpA, and cmpB pulses (qualified by the dir signal) and
generates two internal PWM signals, pwmA and pwmB. In Count-Down mode, there are four events
that can affect these signals: zero, load, match A down, and match B down. In Count-Up/Down
mode, there are six events that can affect these signals: 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 20-5 on page 1078 shows the use of Count-Up/Down mode to generate a pair of
January 22, 2012
Texas Instruments-Production Data
1077