Rabbit RabbitCore RCM2200, Руководство пользователя

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28 RabbitCore RCM2200
4.5 Other Hardware
4.5.1 Clock Doubler
The RCM2200 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 11.0592 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.