Cirrus Logic EP93xx - Manual (Page 735)

DS785UM1 24-3
Copyright 2007 Cirrus Logic
Pulse Width Modulator
EP93xx User’s Guide
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24
24.2.1.3 Dynamic Programming (PWM is Running) Example
Note: Updates will take place at the end of the PWM cycle. Order of programming of the
Terminal Count and Duty Cycle is important. See Section 24.2.2 on page 24-3 .
24.2.2 Programming Rules
1. Because the user can not tell the state of the PWM between cycles, care must be taken
while programming on the fly (while the PWM is running). To insure proper operation
observe the following rules to preserve the relationship of PWMxDutyCycle to
PWMxTermCnt:
A. If PWMxTermCnt (new) > PWMxTermCnt (current):
Program PWMxTermCnt (new) first then PWMxDutyCycle (new)
B. If PWMxTermCnt (new) < PWMxTermCnt (current):
Program PWMxDutyCycle (new) first then PWMxTermCnt (new)
If the rules “A” and “B” are not followed, a duty cycle of 100% may result until both
PWMxTermCnt and PWMxDutyCycle are updated.
2. Program PWMxTermCnt and PWMxDutyCycle with values that meet the specification.
3. When PWM is stopped (PWM_EN = 0), it does not stop immediately but waits for the
end of the current PWM cycle and then stops.
24.3 Registers
Note: All pwmout outputs will drive a logical “0” during reset. Coming out of reset, it will continue
to drive a logical “0”, and the PWM will be in halt mode.
Table 24-2. Dynamic Programming Steps
Step Register Value
Program TC value with 659 PWMxTermCnt 0x0293
Program DC value with 131 PWMxDutyCycle 0x0081
Table 24-3. PWM Registers Map
Address Register Name Reset Value Access Size
0x8091_0000 PWM0TermCnt PWM0 Terminal Count 0x0000 R/W 16
0x8091_0004 PWM0DutyCycle PWM0 Duty Cycle 0x0000 R/W 16
0x8091_0008 PWM0En PWM0 Enable 0x0000 R/W 16
0x8091_000C PWM0Invert PWM0 Invert 0x0000 R/W 16
0x8091_0020 PWM1TermCnt PWM1 Terminal Count 0x0000 R/W 16
0x8091_0024 PWM1DutyCycle PWM1 Duty Cycle 0x0000 R/W 16
0x8091_0028 PWM1En PWM1 Enable 0x0000 R/W 16
0x8091_002C PWM1Invert PWM1 Invert 0x0000 R/W 16