Digi JACKRABBIT BL1800 - Manual (Page 38)

34 Jackrabbit (BL1800)
3.8 Other Hardware
3.8.1 External Interrupts
Jackrabbit boards that carry the CE mark have external interrupts available on digital
inputs PE4 and PE5.
3.8.2 Clock Doubler
Jackrabbit BL1810 and BL1820 models take advantage of the Rabbit 2000 microproces-
sor’s internal clock doubler. A built-in clock doubler allows half-frequency crystals to be
used to reduce radiated emissions. The 14.74 MHz frequency is generated using a
7.37 MHz resonator. The clock doubler is disabled automatically in the BIOS for crystals
or resonators with a frequency above 12.9 MHz.
The clock doubler may be disabled if 14.74 MHz clock speeds are not required. Disabling
the Rabbit 2000 microprocessor’s internal clock doubler will reduce power consumption
and further reduce radiated emissions. Disable the clock doubler by adding a simple con-
figuration 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.