The IECCPUWFIACK input is used by the IEC as an acknowledgement that the processor has executed the WFI command. That is, it has entered sleep mode and ceased all activity on the bus. When a HIGH level on this input is seen, the IEC sets the target performance index outputs IECTGTDVCIDX and IECTGTDCGIDX, to the minimum index level. The IEC does not request the clock to be stopped or the voltage to be lowered until the CPU has acknowledged that it has entered sleep mode by asserting the IECCPUWFIACK signal