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E-1
A P P E N D I X
E
Power Reset and Initialization
Sequences
This appendix describes the power-on and power-off reset sequences.
■
Section E.1, “Power-On Reset Sequence” on page E-1
■
Section E.2, “Power-Off Sequence” on page E-4
E.1 Power-On Reset Sequence
The power-on sequence is initiated as soon as power is applied or when the power
button is pushed, depending on the BIOS settings.
When the sequence is initiated, the main power supplies are enabled, then the
hot-swap circuit for the main 12V rail is enabled. When 12V is up, the supplies are
sequenced as follows:
■
1.5V, 3.3V, and -12V
■
1.8V, 2.5V, and 1.25V
■
Processor core voltage
■
1.2V and 1.5V
When all of the rails are within 5%, the voltage monitor chip waits for 210 mS then
asserts ALL_POWERGOOD, which starts the boot sequence.
The diagram in
FIGURE E-1
shows the power-on sequence.
TABLE E-1
defines the
symbols used in the diagram and describes the power-on sequence timing parameters.