RabbitCore RCM3305, User Manual

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User’s Manual 35
4.4 Other Hardware
4.4.1 Clock Doubler
The RCM3305/RCM3315 takes advantage of the Rabbit 3000 microprocessor’s internal
clock doubler. A built-in clock doubler allows half-frequency crystals to be used to reduce
radiated emissions. The 44.2 MHz frequency specified for the RCM3305/RCM3315 is
generated using a 22.12 MHz resonator.
The clock doubler may be disabled if 44.2 MHz clock speeds are not required. This will
reduce power consumption and further reduce radiated emissions. The clock doubler is
disabled with a simple configuration macro as shown below.
4.4.2 Spectrum Spreader
The Rabbit 3000 features a spectrum spreader, which helps to mitigate EMI problems. The
spectrum spreader is on by default, but it may also be turned off or set to a stronger setting.
The means for doing so is through a simple configuration macro as shown below.
NOTE: Refer to the Rabbit 3000 Microprocessor User’s Manual for more information
on the spectrum-spreading setting and the maximum clock speed.
1. Select the “Defines” tab from the Dynamic C Options > Project Options menu.
2. Add the line
CLOCK_DOUBLED=0
to always disable the clock doubler.
The clock doubler is enabled by default, and usually no entry is needed. If you need to
specify that the clock doubler is always enabled, add the line
CLOCK_DOUBLED=1
to
always enable the clock doubler.
3. Click OK to save the macro. The clock doubler will now remain off whenever you are
in the project file where you defined the macro.
1. Select the “Defines” tab from the Dynamic C Options > Project Options menu.
2. Normal spreading is the default, and usually no entry is needed. If you need to specify
normal spreading, add the line
ENABLE_SPREADER=1
For strong spreading, add the line
ENABLE_SPREADER=2
To disable the spectrum spreader, add the line
ENABLE_SPREADER=0
NOTE: The strong spectrum-spreading setting is unnecessary for the RCM3305/RCM3315.
3. Click OK to save the macro. The spectrum spreader will now be set to the state specified
by the macro value whenever you are in the project file where you defined the macro.