Intel
®
81341 and 81342—DDR SDRAM Memory Controller
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
618
Order Number: 315037-002US
7.4.2
Power Failure Sequence
illustrates the sequence of events during a power failure as defined by
PCI
Local Bus Specification
, Revision 2.2.
7.4.2.1
Power Failure Impact on the System
Upon initial power-up a power supply provides the appropriate voltage to the system.
The voltage level increases at a rate that is dependent on the type of power supply
used and the components in the system. These variables are not certain, so the power
supply often provides a signal called
PWRGD
which indicates the time when the
voltage has reached a reliable level. The power supply deasserts
PWRGD
when the
voltage level drops below a certain minimum threshold.
PCI Local Bus Specification
, Revision 2.2 indicates that once
PWRGD
is deasserted, the
PCI reset pin (
P_RST#
) is asserted in order to float the output buffers. In the
specification T
fail
is defined as the time when
P_RST#
is asserted in response to the
power rail going out of specification. T
fail
is the minimum of:
• 500 ns from either power rail going out of specification (exceeding specified
tolerances by more than 500mV).
• 100 ns from the 5V rail falling below the 3.3V rail by more than 300mV.
7.4.2.2
System Assumptions
This proposal makes specific assumptions about the system behavior during a power
failure. When the below assumptions are not insured, it is the vendor responsibility to
ensure them.
1.
P_RST#
is asserted to the 81341 and 81342 when there is at least 2
µ
s of reliable
power remaining. This is required so that the memory controller can execute its
power-failure state machine in response to the assertion of
P_RST#
.
Figure 96. Power Failure Sequence
Initial
Power-Up
System
Deasserts
CLK
POWER
PWRGD
P_RST#
SCKE
approximately 1 ms
PULLCKE
SCKEout
Power Detected
Good by Supply
Reset
Power
Failure
Power
Restored
Note: PWRGD is shown for reference and is not an Intel® 8134x pin.
B6263-01