Rabbit BL2020, Руководство пользователя

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32 Wildcat (BL2000)
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 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.