Intel SA-1100 9.5.4 Notes on Power Supply Sequencing, 9.5.5 Assumed Behavior of an SA-1100 System in Sleep Mode

9-30 SA-1100

Developer’s Manual

System Control Module

Also, the SA-1100 provides the power manager scratchpad register (PSPR) for saving any general

processor state during sleep. This register may be written by the processor and the contents will

survive sleep mode. The bits in this register are not explicitly used by the SA-1100, but may be

used by software to index into ROM space to retrieve memory controller configuration, for

example.

Note: The nRESET pin must not be asserted during sleep mode if the DRAM contents are to be

preserved. The assertion and subsequent negation of nRESET during sleep mode causes the

SA-1100 to clear the FS bit in the force sleep register, assert PWR_EN, time the PLL lock

sequence, and subsequently negate the internal reset signal. This causes the SA-1100 to perform a

normal boot sequence because all information about the previous sleep state is lost.

Because the DRAMs are placed in self refresh prior to the sleep mode shutdown, their contents are

preserved during sleep. After exiting sleep, software must reconfigure the DRAM control registers,

which lost power during sleep mode, and then take the DRAMs out of self-refresh mode. Clearing

the DRAM hold (DH) bit in the power management status register (PMSR) will cause the

RAS<3:0> and CAS<3:0> pins to return to the negated state (high) in preparation for a DRAM

access.

9.5.4 Notes on Power Supply Sequencing

On the SA-1100, as on the SA-110, it is important that VDDX (3.3V nominal) power-up occur

before VDDI (1.5V nominal). One approach to ensuring this sequencing is to power the 1.5-V

supply using the 3.3-V supply. On the SA-1100, a second simple option is available. If the

PWR_EN output is used to enable the 1.5-V supply, the SA-1100 will enforce the required

sequencing by holding PWR_EN deasserted until the 3.3-V supply is sufficiently high.

9.5.5 Assumed Behavior of an SA-1100 System in Sleep Mode

The assumed model of an SA-1100 system in sleep mode is one in which the system is relatively

quiet. In particular, there should be no gratuitous switching on of the SA-1100 input pins. Alt hough

there will be some switching in GPIOs to bring the processor out of sleep and potentially on the

VDD_FAULT and BATT_FAULT pins, the switching is a low-frequency activity and usually

brings the SA-1100 out of sleep mode.

The major concern is for power dissipation in sleep and requirements for the power supplies on the

processor during sleep. The SA-1100 generates these supplies using several on-chip regulators wi th

limited current capacity. Excessive activity on-chip pins might load these regulators beyond their

capacity and result in droop of the on-chip supplies. One example is that of a component tied to one

of the GPIO pins that constantly transmits to the processor. If the system design indicated that

activity from this detector should not bring the SA-1100 out of sleep, the transitions from this

GPIO might result in switching in the processor that would exceed the sleep current limit. This

concern exists regardless of whether the GPIO is enabled as a wake-up source.

Figure9-3 shows the three power-related modes of the SA-1100 and the actions that cause

transitions between the modes. Table 9 -2 summarizes what power and clock supplies are used by

each module within the SA-1100, as well as the status of the power and clock supplies to each unit

during each of the three power-related modes.