668-0003-C Rabbit Semiconductor, 668-0003-C Datasheet - Page 221

• Manufacturer Part Number: 668-0003-C
• Description: IC CPU RABBIT2000 30MHZ 100PQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0003-C

• Rohs Status: RoHS non-compliant
• Processor Type: Rabbit 2000 8-Bit
• Speed: 30MHz
• Voltage: 2.7V, 3V, 3.3V, 5V
• Mounting Type: Surface Mount
• Package / Case: 100-MQFP, 100-PQFP
• Features: -
• Other names: 316-1004; 668-0003

B.2.12 Clock Spectrum Spreader Module
This is a feature introduced on the Rabbit 3000 and migrated to revisions B and C of the
Rabbit 2000. The clock spectrum spreader and early memory output enable are turned on
by default for the Rabbit 2000C in Dynamic C version 7.32 and higher. The spectrum
spreader is very powerful for reducing EMI because it will reduce all sources of EMI
above 100 MHz that are related to the clock by about 15 dB. This is a very large reduction
since it is common to struggle to reduce EMI by 5 dB in order to pass government tests.
The spectrum spreader modulates the clock so as to spread out the spectrum of the clock
and its harmonics. Since the government tests use a 120 kHz bandwidth to measure EMI,
spreading the energy of a given harmonic over a wider bandwidth will decrease the
amount of EMI measured for a given harmonic. The spectrum spreader not only reduces
the EMI measured in government tests, but it will also often reduce the interference cre-
ated for radio and television reception.
The spectrum spreader has three settings under software control: off, normal spreading,
and strong spreading.
Two registers control the clock spectrum spreader. These registers must be loaded in a spe-
cific manner with proper time delays. GCM0R is only read by the spectrum spreader at the
moment when the spectrum spreader is enabled by storing 0x080 in GCM1R. If GCM1R
is cleared (when disabling the spectrum spreader), there is up to a 500-clock delay before
the spectrum spreader is actually disabled. The proper procedure is to clear GCM1R, wait
for 500 clocks, set GCM0R, and then enable the spreader by storing 0x080 in GCM1R.
Appendix B Rabbit 2000 Revisions
Figure B-2. Peak Spectral Amplitude Reduction from Spectrum Spreader
15 dB
10
5
50
Normal Spreading
100
Strong Spreading
150
MHz
200
250
300
350
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