Rabbit 6000 User’s Manual
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22
2.3.3 Spectrum Spreader
When enabled, the spectrum spreader stretches and compresses the main clock in a complex pattern that
spreads the energy of the clock harmonics over a wider range of frequencies. Note that the spectrum
spreader cannot operate at frequencies above 115 MHz as it uses up too much of the available clock
period, so care must be exercised when using the main PLL.
Figure 2.1 Effects of Spectrum Spreader
There are three settings that correspond to normal and strong spreading in the 0–50 MHz and >50 MHz
main clock range. Each setting will affect the clock cycle differently; the maximum cycle shortening (at
1.8 V and 25°C) is shown in Table 2-4 below.
Table 2-4. Spectrum Spreader Settings
0–50 MHz
50 - 150 MHz
GCM0R
Value
Description
Max. Cycle
Shortening
—
Normal
01xxxxxx
Normal spreading of frequencies
over 50 MHz
2.3 ns
Normal
Strong
00xxxxxx
Normal spreading of frequencies
up to 50 MHz; strong spreading of
frequencies over 50 MHz
3 ns
Strong
—
10xxxxxx
Strong spreading of frequencies up
to 50 MHz; normal spreading of
frequencies over 50 MHz
4.5 ns
Summary of Contents for 6000
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