Intel 80312 I/O Companion Chip - ECEE

Intel ® 80312 I/O Companion ChipMemory Controller3.3.3.1 External Logic Required for Power FailureAssertion of P_RST# During Power FailureUnfortunately, the Intel ® 80312 I/O companion chip does not function down to the minimumvoltage level of 2.5 volts after which the PCI specification guarantees P_RST# is asserted during apower failure. As a result, when the power failure mechanism is to be used, the P_RST# input pinmust be an OR function of the system’s P_RST# signal and the output of a voltage detection circuitthat triggers below the 3.0 volts guaranteed by the PCI specification during normal operations butabove the 2.5 volts where the device is not functional.SCKE ControlRefer to Figure 3-23 for a state machine of the external logic required to control SCKE[1:0] forpower failure mode. Actual implementations may vary. This state machine can be implemented ina programmable logic device illustrated in Figure 3-24.Figure 3-23.External Power Failure State MachineSCKEoutPULLCKE = 1PULLCKE = 0P_RST#A6814-01Developer’s Manual 3-39