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Rabbit 6000 User’s Manual
digi.com
340
30. P
ULSE
W
IDTH
M
ODULATOR
30.1 Overview
The Pulse Width Modulator (PWM) consists of a 10-bit free running counter and four width registers. A
PWM output consists of a train of periodic pulses within a 1024-count frame with a duty cycle that varies
from 1/1024 to 1024/1024. Each PWM output is high for
n
+ 1 counts out of the 1024-clock count cycle
starting when the counter is 0, where
n
is the value held in the width register. Any changes to the width
registers will not take effect until the next counter rollover.
The PWM is clocked by the output of Timer A9 which is used to set the period. Timer A9 can be further
prescaled by cascading it off of Timer A12.
Each PWM output high time can optionally be spread throughout the cycle to reduce ripple on the exter-
nally filtered PWM output. The PWM outputs can be passed through a filter and used as a 10-bit D/A con-
verter. The outputs can also be used to directly drive devices such as motors or solenoids that have intrinsic
filtering.
The PWM outputs can trigger a PWM interrupt when the counter rolls over to zero on every PWM cycle,
every other cycle, every fourth cycle, or every eighth cycle. In addition, the PWM output can be sup-
pressed every other cycle, three out of every four cycles, or seven out of every eight cycles. These options
provide support for driving servos and to generate audio signals. The setup for this interrupt is done in the
PWL0R and PWL1R registers. The timing is shown below.
Summary of Contents for 6000
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