BL4S100 User’s Manual
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3.6 Other Hardware
3.6.1 Clock Doubler
The BL4S100 takes advantage of the Rabbit microprocessor’s internal clock doubler. A
built-in clock doubler allows half-frequency crystals to be used to reduce radiated emissions.
The clock doubler may be disabled if the higher clock speeds are not required. Disabling
the clock doubler will reduce power consumption and further reduce radiated emissions.
The clock doubler is disabled with a simple configuration macro as shown below.
3.6.2 Spectrum Spreader
The Rabbit microprocessors features a spectrum spreader, which help to mitigate EMI
problems. By default, the spectrum spreader is on automatically, but it may also be turned
off or set to a stronger setting. The means for doing so is through a simple configuration
macro as shown below.
NOTE:
Refer to the
Rabbit 4000 Microprocessor User’s Manual
for more information
on the spectrum-spreading settings and the maximum clock speed.
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.
3. Click
OK
to save the macro. The clock doubler will now remain off or on according to
your setting whenever you are using the project file where you defined the macro.
1.
Select the “Defines” tab from the Dynamic C
Options > Project Options
menu.
2. Normal spreading is the default, and usually no entry is needed. If you need to specify nor-
mal spreading, add the line
ENABLE_SPREADER=1
For strong spreading, add the line
ENABLE_SPREADER=2
To disable the spectrum spreader, add the line
ENABLE_SPREADER=0
NOTE:
The strong spectrum-spreading setting is not recommended since it may limit
the maximum clock speed or the maximum baud rate. It is unlikely that the strong set-
ting will be used in a real application.
3.
Click
OK
to save
the macro. The spectrum spreader will be set according to the macro
value whenever a program is compiled using this project file.
