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3.4 Other Hardware
3.4.1 Clock Doubler
The Smart Star CPU cards take advantage of the Rabbit 2000 microprocessor ’s internal
clock doubler. A built-in clock doubler allows half-frequency crystals to be used to reduce
radiated emissions. The 22.1 MHz frequency is generated using an 11.0592 MHz crystal.
The clock doubler is disabled automatically in the BIOS for crystals with a frequency
above 12.9 MHz.
The clock doubler may be disabled if 22.1 MHz clock speeds are not required. Disabling
the Rabbit 2000 microprocessor ’s internal clock doubler will reduce power consumption
and further reduce radiated emissions. The clock doubler is disabled with a simple config-
uration macro as shown below.
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. The clock speed will be doubled as long as the crystal frequency is
less than or equal to 26.7264 MHz.
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.
3.4.2 Spectrum Spreader
Smart Star CPU cards that carry the CE mark have a Rabbit 2000 microprocessor that fea-
tures a spectrum spreader, which helps to mitigate EMI problems. By default, the spectrum
spreader is on automatically for CPU cards that carry the CE mark when used with Dynamic C
7.32 or later versions, but the spectrum spreader 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.
.
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 Smart Star.
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.
There is no spectrum spreader functionality for Smart Star CPU cards that do not carry the
CE mark or when using any CPU card with a version of Dynamic C prior to 7.30.
User ’s Manual
41
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