Digi BL1800 user manual Other Hardware, External Interrupts, Clock Doubler

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

7.37MHz 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.

34 Jackrabbit (BL1800)