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PowerCore FLEX
4.5 Other Hardware
4.5.1 Clock Doubler
The PowerCore 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 51.6 MHz frequency specified for the PowerCore is generated using a
25.8 MHz crystal.
The clock doubler may be disabled if 51.6 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.
The clock doubler is automatically off for 25.8 MHz modules. Fast SRAM is needed to
run programs when clock speeds are above 30 MHz.
4.5.2 Spectrum Spreader
The Rabbit 3000 features a spectrum spreader, which helps to mitigate EMI problems. By
default, the spectrum spreader is on automatically, 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.
TIP: If you wish to add more than one macro definition to the Global Macro Definitions
box, the macros should be separated by semi-colons.
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 nor-
mal 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 not recommended since it may limit
the maximum clock speed or the maximum baud rate. It is unlikely that the strong
setting will be used in a real application.
3. Click OK to save the macro. The spectrum spreader will now remain off whenever you are
in the project file where you defined the macro.