AMD SC1201, SC1200 manual System Power States

SuperI/O Module 32579B

5.5.2.7System Power States

The system power state may be No Power, Power On, Power Off or Power Failure. Table 5-18indicates the power- source combinations for each state. No other power-source combinations are valid.

In addition, the power sources and distribution for the entire system are illustrated in Figure 5-8 on page 108.

Table 5-18. System Power States

VDIGITAL	VSB	VBAT	Power State
−	−	−	No Power
−	−	+	Power Failure
−	+	+ or -	Power Off
+	+	+ or -	Power On

No Power

This state exists when no external or battery power is con- nected to the device. This condition does not occur once a backup battery has been connected, except in the case of a malfunction.

Power On

This is the normal state when the system is active. This state may be initiated by various events in addition to the normal physical switching on of the system. In this state, the system power supply is powered by external AC power

and produces VDIGITAL and VSB. The system and the part are powered by VDIGITAL, with the exception of the RTC log- ical device, which is powered by VSB.

Power Off (Suspended)

This is the normal state when the system has been switched off and is not required to be active, but is still con- nected to a live external AC input power source. This state may be initiated directly or by software. The system is pow- ered down. The RTC logical device remains active, pow- ered by VSB.

Power Failure

This state occurs when the external power source to the system stops supplying power, due to disconnection or power failure on the external AC input power source. The RTC continues to maintain timekeeping and RAM data under battery power (VBAT), unless the oscillator stop bit was set in the RTC. In this case, the oscillator stops func- tioning if the system goes to battery power, and timekeep- ing data becomes invalid.

System Bus Lockout

During power on or power off, spurious bus transactions from the host may occur. To protect the RTC internal regis- ters from corruption, all inputs are automatically locked out. The lockout condition is asserted when VSB is lower than

VSBON.

Power-Up Detection

When system power is restored after a power failure or power off state (VSB = 0), the lockout condition continues for a delay of 62 msec (minimum) to 125 msec (maximum) after the RTC switches from battery to system power.

The lockout condition is switched off immediately in the fol- lowing situations:

•If the Divider Chain Control bits, DV[2:0], (CRA bits [6:4]) specify a normal operation mode (01x or 100), all input signals are enabled immediately upon detection of system voltage above VSBON.

•When battery voltage is below VBATDCT and HMR is 1, all input signals are enabled immediately upon detection

of system voltage above VSBON. This also initializes registers at offsets 00h through 0Dh.

•If bit 7 (VRT) of CRD is 0, all input signals are enabled immediately upon detection of system voltage above

VSBON.

5.5.2.8Oscillator Activity

The RTC oscillator is active if:

•VSB power supply is higher than VSBON, independent of the battery voltage, VBAT

-or-

•VBAT power supply is higher than VBATMIN, regardless if VSB is present or not.

The RTC oscillator is disabled if:

•During power-down (VBAT only), the battery voltage drops below VBATMIN. When this occurs, the oscillator may be disabled and its functionality cannot be guaran- teed.

-or-

•Software wrote 00x to DV[2:0] bits of the CRA Register

and VSB is removed. This disables the oscillator and decreases the power consumption from the battery

connected to VBAT. When disabling the oscillator, the CMOS RAM is not affected as long as the battery is present at a correct voltage level.

If the RTC oscillator becomes inactive, the following fea- tures are dysfunctional/disabled:

•Timekeeping.

•Periodic interrupt.

•Alarm.

AMD Geode™ SC1200/SC1201 Processor Data Book 109