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Chapter 7 CPU power consumption
The main goal of Soft Power Management is to reduce CPU power consumption when not needed.
This chapter compares the power consumption of a CPU-1450 with Celeron 400MHz and 256MB SDRAM
running in standard mode and some sleep or low power modes.
The following table list the CPU-1450 power consumption in the different states:
CPU-1450 w/ Celeron 400MHz and 256MB SDRAM
Power mode Ethernet connection Power consumption typical
Full power mode Negligible 8.00 W
Soft-off or suspend-to-disk sleep mode Ethernet disabled 0.35 W
Soft-off or suspend-to-disk sleep mode Cable disconnected 0.75 W
Soft-off or suspend-to-disk sleep mode Link at 10 MBIT 0.68 W
Soft-off or suspend-to-disk sleep mode Link at 100 MBIT 0.90 W
Table 17. CPU-1450 Power Consumption
We can see that the energy saving with low power / sleep mode is very high.
The disadvantage is that it needs an ATX-like power supply with two supplies for working with the SPM
mode:
A main supply (VDD) that could be turned on and off by software.
An auxiliary supply (+5VSB) that is always present. The whole power consumption in sleep mode is
taken from this power line.
Warning:
Once the auxiliary power is on, the board is always supplied so take care to handle it.
Without an ATX-like power supply the CPU-1450 Module could not work with SPM and the Power keeps all
the board on.