AMD AMD-K6-2/400 User Guide - Page 173
Dynamic Core, Frequency Control, Voltage Identification, VID Outputs
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23542A/0-September 2000 Preliminary Information AMD-K6™-2E+ Embedded Processor Data Sheet Dynamic Core Frequency Control Voltage Identification (VID) Outputs For AMD PowerNow! technology core frequency transitions, the BVC field of the EPM 16-byte I/O block is accessed through an SMM handler. s To change the processor core frequency, the SMM handler initiates core voltage and frequency transitions by writing a non-zero value to the SGTC field. s This action automatically places the processor into the EPM Stop Grant state and transitions the CPU core voltage and frequency to the values specified in the VIDO and IBF fields of the BVC field. Note: System-initiated inquire (snoop) cycles are not supported and must be prevented during the EPM Stop Grant state. AMD PowerNow! technology-enabled processors feature Voltage ID (VID) outputs to support dynamic control of the core voltage. s These outputs serve as inputs to a DC/DC regulator that supplies the processor core voltage. s Based on its VID[4:0] inputs, the regulator outputs a corresponding voltage. s For those regulators that do not support VID inputs, the processor VID[4:0] outputs must be used to manipulate the regulator's feedback voltage to vary the regulator output voltage. Chapter 6 AMD PowerNow!™ Technology 151