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4-38 Intel® PXA255 Processor Developer’s Manual
System Integration Unit
4.5 Pulse Width Modulator
Use the Pulse Width Modulator (PWM) to generate as many as two signals to be output from the
processor. The signals are based on the 3.6864 MHz clock and must be a minimum of 2 clock
cycles wide. These signals are output from the processor by configuring the GPIOs.
4.5.1 Pulse Width Modulator Operation
The processor contains two pulse width modulators: PWM0 and PWM1. Each PWM operates
independently of the other, is controlled by its own set of registers. They provide a pulse width
modulated signal on an external pin. Since each PWM contains identical circuitry, a generic
PWMn, where n is 0 or 1, is described.
Each PWM contains:
• Two Pulse Width Modulator channels
• Enhanced Period control through 6-Bit Clock divider and 10-Bit Period counter
• 10-Bit Pulse control
A block diagram of one of the PWMs is shown in Figure 4-3.
Table 4-45. OSSR Bit Definitions
Physical Address
0x40A0_0014
OS Timer Status Register (OSSR) 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
M3
M2
M1
M0
Reset ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 0 0 0
Bits Name Description
<31:4> — reserved
<3> M3
Match status channel 3.
If OIER[3] is set then:
0 – OSMR[3] has NOT matched the OS timer counter since last being cleared.
1 – OSMR[3] has matched the OS timer counter.
<2> M2
Match status channel 2.
If OIER[2] is set then:
0 – OSMR[2] has NOT matched the OS timer counter since last being cleared.
1 – OSMR[2] has matched the OS timer counter.
<1> M1
Match status channel 1.
If OIER[1] is set then:
0 – OSMR[1] has NOT matched the OS timer counter since last being cleared.
1 – OSMR[1] has matched the OS timer counter.
<0> M0
Match status channel 0.
If OIER[0] is set then:
0 – OSMR[0] has NOT matched the OS timer counter since last being cleared.
1 – OSMR[0] has matched the OS timer counter.