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PULSE-WIDTH MODULATOR |
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Duty |
PWM Control |
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Output Waveform |
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Cycle |
Register Value |
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0% |
00 |
0 |
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10% |
25 |
0 |
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50% |
128 |
0 |
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90% |
230 |
0 |
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99.6% |
255 |
0 |
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A5493-01 |
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Figure 10-2. PWM Output Waveforms
10.4 PROGRAMMING THE FREQUENCY AND PERIOD
The input frequency on XTAL1 (FXTAL1) and the contents of the PWMx_y_PERIOD register determine the PWM output frequency (FPWM) and period (TPWM). Table 10-3 shows the PWM output frequencies for common values of FXTAL1 with a variety of PWMx_y_PERIOD values. Use the following formulas to calculate the PWM period value for the desired output frequency and write
the corresponding value to the PWMx_y_PERIOD register (Figure 10-3 on page 10-7).
TPWM (in μs) = |
P × (PWMx_y_PERIOD + 1) |
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------------------ |
---------------F----XTAL---------1---------------------------------- |
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FPWM (in MHz) = |
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FXTAL1 |
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P------------------× (PWM-----------x----_----y---_----PERIOD---------------------------+----1)----- |
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where: |
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TPWM |
= |
output period on the PWM output pins, in μs |
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FPWM |
= |
output frequency on the PWM output pins, in MHz |
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P |
= |
256 if the phase-locked loop (PLL) circuitry is enabled |
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512 if the phase-locked loop (PLL) circuitry is disabled |
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PWMx_y_PERIOD |
= |
eight-bit value to load into the PWM_PERIOD register |
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FXTAL1 |
= |
input frequency on XTAL1 pin, in MHz |
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10-5
8XC196EA USER’S MANUAL
Table 10-3. PWM Output Frequencies (FPWM)
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FXTAL1 with PLL Enabled |
FXTAL1 with PLL Disabled |
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PWMx_y_PERIOD |
(f† = 2F |
XTAL1 |
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(f = F |
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XTAL1 |
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10 MHz |
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20 MHz |
10 MHz |
20 MHz |
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40 MHz |
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00H |
39.1 KHz |
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78.1 KHz |
19.5 KHz |
39.1 KHz |
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78.1 KHz |
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0FH |
2441.4 Hz |
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4882.8 Hz |
1220.7 Hz |
2441.4 Hz |
4882.8 Hz |
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1FH |
1220.7 Hz |
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2441.4 Hz |
610.4 Hz |
1220.7 Hz |
2441.4 Hz |
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2FH |
813.8 Hz |
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1627.6 Hz |
406.9 Hz |
813.8 Hz |
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1627.6 Hz |
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3FH |
610.4 Hz |
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1220.7 Hz |
305.2 Hz |
610.4 Hz |
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1220.7 Hz |
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4FH |
488.3 Hz |
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976.6 Hz |
244.1 Hz |
488.3 Hz |
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976.6 Hz |
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5FH |
406.9 Hz |
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813.8 Hz |
203.5 Hz |
406.9 Hz |
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813.8 Hz |
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6FH |
348.8 Hz |
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697.5 Hz |
174.4 Hz |
348.8 Hz |
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697.5 Hz |
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7FH |
305.2 Hz |
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610.4 Hz |
152.6 Hz |
305.2 Hz |
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610.4 Hz |
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8FH |
271.3 Hz |
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542.5 Hz |
135.6 Hz |
271.3 Hz |
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542.5 Hz |
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9FH |
244.1 Hz |
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488.3 Hz |
122.1 Hz |
244.1 Hz |
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488.3 Hz |
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AFH |
221.9 Hz |
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443.9 Hz |
111.0 Hz |
221.9 Hz |
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443.9 Hz |
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BFH |
203.5 Hz |
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406.9 Hz |
101.7 Hz |
203.5 Hz |
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406.9 Hz |
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CFH |
187.8 Hz |
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375.6 Hz |
93.9 Hz |
187.8 Hz |
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375.6 Hz |
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DFH |
174.4 Hz |
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348.8 Hz |
87.2 Hz |
174.4 Hz |
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348.8 Hz |
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EFH |
162.8 Hz |
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325.5 Hz |
81.4 Hz |
162.8 Hz |
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325.5 Hz |
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FFH |
152.6 Hz |
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305.2 Hz |
76.3 Hz |
152.6 Hz |
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305.2 Hz |
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† f = internal operating frequency
10-6