Rabbit Rabbit 4000, User Manual

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Chapter 26 Low-Power Operation 271
26. L
OW
-P
OWER
O
PERATION
26.1 Overview
The Rabbit 4000 contains several power-saving features. Since the power consumed by
the processor is proportional to the clock speed, the Rabbit 4000 provides 12 clock modes
that can go as low as 2 kHz. To further reduce power consumption in those ultra-sleepy
modes, various shortened chip select strobes are available to reduce current draw by the
attached memory devices.
Figure 26-1 shows a typical current draw as a function of the main clock frequency. The
values shown do not include any current consumed by external oscillators or memory. It is
assumed that approximately 30 pF is connected to each address line.
Figure 26-1. Typical Current Draw as a Function of the Main Clock Frequency
2 10 20 30 40 50 60
70
60
50
40
30
20
10
0
CPU/PERPHERAL CLOCKS (MHz)
CURRENT (mA)
I
total
I
IO
I
CORE