40 RabbitCore RCM3365/RCM33754.5 Other Hardware4.5.1 Clock DoublerThe RCM3365/RCM33610 takes advantage of the Rabbit 3000 microprocessor’s internalclock doubler. A built-in clock doubler allows half-frequency crystals to be used to reduceradiated emissions. The 44.2 MHz frequency specified for the RCM3365/RCM3375 isgenerated using a 22.12 MHz resonator.The clock doubler may be disabled if 44.2 MHz clock speeds are not required. This willreduce power consumption and further reduce radiated emissions. The clock doubler isdisabled with a simple configuration macro as shown below.4.5.2 Spectrum SpreaderThe Rabbit 3000 features a spectrum spreader, which helps to mitigate EMI problems. Thespectrum 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 informationon 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 tospecify that the clock doubler is always enabled, add the line CLOCK_DOUBLED=1 toalways enable the clock doubler.3. Click OK to save the macro. The clock doubler will now remain off whenever you arein 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 specifynormal spreading, add the lineENABLE_SPREADER=1For strong spreading, add the lineENABLE_SPREADER=2To disable the spectrum spreader, add the lineENABLE_SPREADER=0NOTE: The strong spectrum-spreading setting is not recommended since it may limitthe maximum clock speed or the maximum baud rate. It is unlikely that the strong set-ting will be used in a real application.3. Click OK to save the macro. The spectrum spreader will now be set to the state specifiedby the macro value whenever you are in the project file where you defined the macro.
