668-0011 Rabbit Semiconductor, 668-0011 Datasheet - Page 22

• Manufacturer Part Number: 668-0011
• Description: IC MPU RABIT3000A 55.5MHZ128LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0011

• Rohs Status: RoHS non-compliant
• Processor Type: Rabbit 3000 8-Bit
• Speed: 55.5MHz
• Voltage: 2.5V, 2.7V, 3V, 3.3V
• Mounting Type: Surface Mount
• Package / Case: 128-LQFP
• Features: -
• Other names: 316-1043

The spectrum spreader either stretches or shrinks the low plateau of the clock by a maxi-
mum of 3 ns for the normal spreading and up to 5 ns for the strong spreading. If the clock
doubler is used, this will cause an additional asymmetry between alternate clock cycles.
Both normal and strong modes reduce clock harmonics by approximately 15 dB for fre-
quencies above 100 MHz; for lower frequencies the strong setting has a greater effect in
reducing the peak spectral strength as shown in Figure 2-2.
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.
The spectrum spreader is applied to the main clock before the clock doubler, so if both are
enabled there will be additional asymmetry between alternate clock cycles.If the clock
doubler is used, the spectrum spreader affects every other cycle and reduces the clock high
time. If the doubler is not used, then the spreader affects every clock cycle, and the clock
low time is reduced.
12
Figure 2-2. Peak Spectral Amplitude Reduction by Spectrum Spreader
15
10
5
50
Normal Spreading
100
Strong Spreading
Frequency (MHz)
150
200
Rabbit 3000 Microprocessor User’s Manual
250
300
350