User’s Manual
31
3.9 Other Hardware
3.9.1 External Interrupts
BL2000 boards
with a Rabbit 2000 microprocessor labeled IQ3T or higher have external
interrupts available on digital inputs
IN2 and IN3.
Older BL2000 boards (
Rabbit 2000
microprocessors
labeled IQ2T) have one external interrupt available—see Technical Note
TN301,
Rabbit 2000
Microprocessor Interrupt Problem
, for further information on how
to use this interrupt on
the older boards.
3.9.2 Clock Doubler
The BL2000 takes advantage of the Rabbit 2000 microprocessor’s internal clock doubler.
A built-in clock doubler allows half-frequency crystals to be used to reduce radiated emis-
sions. 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 change
to the BIOS as described below.
3.9.3 Spectrum Spreader
BL2000 boards that carry the CE mark have a Rabbit 2000 microprocessor that features a
spectrum spreader, which helps to mitigate EMI problems. By default, the spectrum
spreader is on automatically for BL2000 boards that carry the CE mark when used with
Dynamic C 7.32 or later versions, but the spectrum spreader may also be turned off or set
to a stronger setting. The means for doing so is through a simple change to the following
BIOS line in a way that is similar to the clock doubler described above.
#define ENABLE_SPREADER 1 // Set to 0 to disable spectrum spreader
// 1 to enable normal spreading, or
// 2 to enable strong spreading.
NOTE:
The strong spectrum-spreading setting is unnecessary for the BL2000.
There is no spectrum spreader functionality for BL2000 boards that do not carry the CE
mark or when using any BL2000 with a version of Dynamic C prior to 7.30.
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
.
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