Other Hardware; Clock Doubler; Spectrum Spreader - Rabbit RabbitCore RCM2200 User Manual

2.4 Other Hardware

2.4.1 Clock Doubler

The RCM2200 takes advantage of the Rabbit 2000 microprocessor's internal clock dou-
bler. A built-in clock doubler allows half-frequency crystals to be used to reduce radiated
emissions. 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.
1. Open the BIOS source code file,
2. Change the line
#define CLOCK_DOUBLED 1 // set to 1 to double the clock if XTAL<=12.9MHz,
to read as follows.
#define CLOCK_DOUBLED 0 // set to 1 to double the clock if XTAL<=12.9MHz,
3. Change the serial baud rate to 57,600 bps when the RabbitCore RCM2200 is operated
at 11.05 MHz.
4. Save the change using

2.4.2 Spectrum Spreader

RCM2200 RabbitCore modules that have a Rabbit 2000 microprocessor labeled IQ4T (or
higher) are equipped with a Rabbit 2000 microprocessor that has a spectrum spreader,
which helps to mitigate EMI problems. By default, the spectrum spreader is on automati-
cally for RCM2200 modules that carry the IQ4T (or higher) marking when used with
Dynamic C 7.30 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
NOTE: The strong spectrum-spreading setting is usually not necessary for the
RCM2200.
There is no spectrum spreader functionality for RCM2200 RabbitCore modules that have
a Rabbit 2000 microprocessor labeled IQ1T, IQ2T, or IQ3T, or when using any RCM2200
with a version of Dynamic C prior to 7.30.
12
RABBITBIOS.C
File > Save .
// Set to 0 to disable spectrum spreader
// 1 to enable normal spreading, or
// 2 to enable strong spreading.
in the directory.
BIOS
RabbitCore RCM2200