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Geode GXLV Processor Series Low Power Integrated x86 Solutions

Geode GXLV Processor Series Low Power Integrated x86 Solutions

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<strong>Geode</strong> <strong>GXLV</strong> <strong>Processor</strong> <strong>Series</strong><strong>Power</strong> Management (Continued)5.2.3 Stopping the Input ClockThe <strong>GXLV</strong> processor is a static device, allowing the inputclock (SYSCLK) to be stopped and restarted without anyloss of internal CPU data. The SYSCLK input can bestopped at either a logic high or logic low state. Therequired sequence for stopping SYSCLK is to initiate 3Volt Suspend, wait for the assertion of SUSPA# by theprocessor, and then stop the input clock.The CPU remains suspended until SYSCLK is restartedand the Suspend mode is exited as described earlier.While SYSCLK is stopped, the processor can no longersample and respond to any input stimulus includingREQx#, NMI, SMI#, INTR, and RESET inputs.Figure 5-4 illustrates the recommended sequence forstopping the SYSCLK using SUSP# to initiate 3 Volt Suspend.SYSCLK may be started prior to or following negationof the SUSP# input. The figure includes theSUSP_3V pin from the <strong>Geode</strong> I/O companion which isused to stop the external clocks.5.2.4 Serial Packet TransmissionThe <strong>GXLV</strong> processor transmits the contents of the “PMSerial Packet Register” on the SERIALP output pin to thePSERIAL input pin of the <strong>Geode</strong> I/O companion. The<strong>GXLV</strong> processor holds SERIALP low until the transmissioninterval counter (GX_BASE+8504h[4:3]) haselapsed. Once the counter has elapsed, PSERIAL is heldhigh for two SYSCLKs to indicate the start of packet transmission.The contents of the packet register are then shifted outstarting from bit 7 down to bit 0. PSERIAL is held high forone SYSCLK to indicate the end of packet transmissionand then remains low until the next transmission interval.After the packet transmission has completed, the packetcontents are cleared.SYSCLKSUSP#SUSPA#SUSP_3V(I/O companion)SMI Event, Timer or PinFigure 5-4. Stopping SYSCLK During Suspend Modewww.national.com 180 Revision 1.3

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