18-2
MCF5272 User’s Manual
PWM Operation
Summary of the main features include:
•
Double-buffered width register
•
Variable-divide prescale
•
Three independent PWM modules
•
Byte-wide width register provides programmable duty cycle control
18.2 PWM Operation
The PWM is a simple free-running counter combined with a pulse width register and a
comparator such that the output is cleared whenever the counter value exceeds the width
register value. When the counter overflows, or “wraps around,” its value becomes less than
or equal to the value of the width register, and the output is set. With a suitable low-pass
filter, the PWM can be used as a digital-to-analog converter.
The width register is double-buffered so that a new value can be loaded for the next cycle
without affecting the current cycle. At the beginning of each period, the value of the width
buffer register is loaded into the width register, which feeds the comparator. This value is
used for comparison during the next cycle. The prescaler contains a variable divider that
can reduce the incoming clock frequency by certain values between 1 and 32768.
18.3 PWM Programming Model
This section describes the registers and control bits in the PWM module. There are three
independent PWM modules, each with its own control and width registers. The memory
map for the PWM is shown in Table 18-1.
Table 18-1. PWM Module Memory Map
MBAR
Offset
[31:24]
[23:16]
[15:8]
[7:0]
0x00C0
PWM Control Register 0
Reserved
0x00C4
PWM Control Register 1
Reserved
0x00C8
PWM Control Register 2
Reserved
0x00D0
PWM Pulse Width Register
Reserved
0x00D4
PWM Pulse Width Register
Reserved
0x00D8
PWM Pulse Width Register
Reserved
Содержание DigitalDNA ColdFire MCF5272
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Страница 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
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