Digi NS9215 - Manual (Page 145)

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S Y S T E M C O N T R O L M O D U L E
Enhanced PWM function
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E n h a n c e d P W M f u n c t i o n
Timer counters 6–9 have additional features to add enhanced PWM functionality:
High register — Compared to the timer/counter to toggle PWM output high
Low register — Compared to the timer/counter to toggle PWM output back low
Three 15-bit Step registers associated with four enhanced timer/counters. The
values of Step registers are added when the high, low, and reload values are
reached, which allows a steadily variable motor control PWM wave to be
generated. The enhanced PWM function is output through GPIO through the
functions labeled Ext Timer Event Out Ch N for channels 6 to 9.
Sample enhanced
PWM waveform
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Q u a d r a t u r e d e c o d e r f u n c t i o n
The processor provides a quadrature decoder function to allow the CPU to
determine the external device rate of rotation and the direction of rotation.
Example applications are robotic axles for feedback control, mechanical knobs to
determine user input, and in computer mice, to determine direction of movement.
One timer/counter will include a quadrature decoder function, which takes some
computational load off the CPU. When a CPU reads the output signals of a
quadrature encoder, every state must be decoded and a counter needs to be
updated based on the interpretation of the states. For example, for an encoder of
256 pulses per revolution turning at a modest 6000 rpm, the CPU needs to find and
decoded 102,400 state changes per second and update the counter accordingly.
With an x8 sampling rate, the CPU needs to sample the input about 8 x 102,400
timer per second. This consumes a significant portion of the CPU bandwidth.
Timer Counter clock frequency
PWM period
Low time 1
High time
Low time 2 75MHz
873.000 usec
382.293 usec
218.453 usec
272.254 usec
Reload Value
FFFF_0000
High Value
FFFF_7000
High Value
FFFF_B000
Terminal Count
FFFF_FFFF