User`s manual

User’s Manual 35
4.5 Other Hardware
4.5.1 Clock Doubler
The RCM2100 takes advantage of the Rabbit 2000 microprocessor’s internal clock dou-
bler. 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 11.05 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 will reduce power consumption and fur-
ther reduce radiated emissions. The clock doubler is disabled with a simple configuration
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.