Z-World BL1800, User Manual

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24 Jackrabbit (BL1800)
2.7 Other Hardware
2.7.1 External Interrupts
Jackrabbit boards that carry the CE mark have external interrupts available on digital
inputs PE4 and PE5.
2.7.2 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 14.7 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 14.7 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 change
to the BIOS as described below.
1. Open the BIOS source code file,
RABBITBIOS.C
in the
BIOS
directory.
2. Change the line
#define CLOCK_DOUBLED 1 // set to 1 to double clock if
// Rabbit 2000: crystal <= 12.9024 MHz,
// Rabbit 3000: crystal <= 26.7264 MHz,
// or to 0 to always disable clock doubler
to read as follows.
#define CLOCK_DOUBLED 0
3. Save the change using
File > Save
.