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4-42 Intel® PXA255 Processor Developer’s Manual
System Integration Unit
4.5.2.3 PWM Period Control Register (PWM_PERVALn)
The PWM_PERVALn, shown in Table 4-48, contains a 10 bit field called PV. This field determines
the period of the PWM_OUTn waveform in terms of the PSCLK_PWMn clock. If this field is
cleared to zero PWMn is effectively turned off and PWM_OUTn remains in a high state. For any
non-zero value written to the PV field, the output frequency of PWMn is the frequency of the
PSCLK_OUTn divided by the value of (PV + 1). The range of the clock gate extends from a pass-
through of the PSCLK_PWMn to a clock delay of 2
6
or 64 input clocks per output pulse.
When the value of the 10 bit up-counter equals the value of (PV +1), the up-counter and the flip-
flop are reset and the values of PWM_CTRLn, PWM_PERVALn and PWM_DUTYn are loaded
into the internal versions of these registers. Resetting this flip-flop causes PWM_OUTn to go low
and the PWM cycle to start again.
Writing all zeroes to this register results in the output maintaining a high state unless
FDCYCLE=0x0 and DCYCLE=0x0. If FDCYCLE=0x0 and DCYCLE=0x0, the output maintains
a low state regardless of the value in the PV bit field.
Note: Due to internal timing requirements, all changes to any of the PWM registers must be complete a
minimum of 4 core clock cycles before the start of end of a PWM clock cycle in order to guarantee
that the following PWM cycle implements the new values.
Table 4-47. PWM_DUTYn Bit Definitions
Physical Address
0x40B0_0004
0x40C0_0004
PWM Duty Cycle Registers
(PWM_DUTY0, PWM_DUTY1)
System Integration Unit
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved
FDCYCLE
DCYCLE
Reset
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bits Name Description
<31:11> — reserved
<10> FDCYCLE
PWMn Full Duty Cycle
0 – PWM clock (PWM_OUTn) duty cycle is determined by DCYCLE field.
1 – PWM_OUTn is set high and does not toggle.
<9:0> DCYCLE
PWMn Duty Cycle
Duty cycle of PWMn clock, i.e. the number of PSCLK_PWM cycles PWMn is asserted
within one cycle of PWMn.