User`s manual

32 RabbitCore RCM2000
4.5 Other Hardware
4.5.1 Clock Doubler
The RCM2000 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 25.8 MHz (RCM 2000 and RCM2010) and 18.4 MHz (RCM 2020) fre-
quencies are generated using 12.9 MHz and 9.2 MHz crystals. The clock doubler is dis-
abled automatically in the BIOS for crystals with a frequency above 12.9 MHz.
The clock doubler can be disabled if 25.8 MHz or 18.4 MHz clock speeds are not required.
Disabling the Rabbit 2000 microprocessor’s internal clock will reduce power consumption
and further reduce radiated emissions. The clock doubler is disabled with a simple config-
uration macro as shown below.
Change the serial baud rate to 57,600 bps when the RCM2000 is operated at 12.9 MHz or
9.2 MHz.
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.