User`s manual

30 RabbitCore RCM2300
4.4 Other Hardware
4.4.1 Clock Doubler
The RCM2300 takes 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 emis-
sions. The 22.1 MHz frequency is generated using an 11.0592 MHz crystal. The clock dou-
bler 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.
4.4.2 Spectrum Spreader
RCM2300 boards with a Rabbit 2000 microprocessor labeled IQ4T or higher have a spec-
trum spreader, which helps to mitigate EMI problems. By default, the spectrum spreader is
on automatically for these boards when used with Dynamic C 7.30 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.
There is no spectrum spreader functionality for RCM2300 boards with Rabbit 2000 chips
labeled IQ3T or earlier, or with a version of Dynamic C prior to 7.30.
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.
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 not necessary for the RCM2300.
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.