ELANSC310 datasheet(47/119 Pages) AMD

47 / 119 page

Élan™SC310 Microcontroller Data Sheet

PREL IMINARY

The RESIN pin acts as the master reset. When active,

all of the internal components are reset, including the

RTC, and the RTC RAM invalid bit will be set. This

causes an issue with the power-loss bit (VRT), Index

0Dh, bit 7 of the RTC map. The VRT bit is intended to

provide a method of determining when the RTC core

voltage supply has dropped below an acceptable level.

On a 146818A-compatible device, anything below

2.4 V will cause a low-battery condition and will cause

the power-loss bit to go Low. On the ÉlanSC310 micro-

controller, the 32-KHz clock used by RTC to maintain

time stops oscillating before the VRT bit or RAM con-

tents get cleared because the VRT bit will only get

cleared when the RESIN pin is asserted Low. Thus, the

RTC time will be inaccurate even though the RAM con-

tents are valid and the VRT bit is still set.

Note: Although the 32-KHz clock stops oscillating be-

fore the power-loss bit is cleared, this event occurs well

before the 2.4-V specification for proper ÉlanSC310

microcontroller functionality.

The RESIN pin should only be asserted (pulsed) Low

when a power source is initially applied to the device’s

core and analog sections.

For more information about these notes, see the

ÉlanTMSC300 and ÉlanTMSC310 Microcontrollers Solu-

tion For Systems Using a Back-up Battery Application

Note

, order #20746.

The IORESET signal is intended to be the normal

“POWER GOOD” status from the primary power supply

in the example design shown in Figure 3. The IORE-

SET input does not reset the RTC and will not set the

RTC RAM invalid bit.

IORESET (when the inactive state is detected) will

cause the ÉlanSC310 microcontroller to go through its

power-up sequence including PLL start-up for clock

generation and an internal CPU reset. See Figure 32

through Figure 35, beginning on page 89, for the initial

power-up timing requirements and for Micro Power

mode exit timing.

When entering Micro Power Off mode and the primary

power supply outputs are turned off, all of the

ÉlanSC310 microcontroller’s powered-down I/O pins

are essentially tri-stated and the internal pull-ups are

removed because the VCCIO and VCC CLAMP of the

output driver have been removed, as shown in Figure

34 on page 91. This provides the ability to power off ex-

ternal peripherals that are attached directly to the

ÉlanSC310 microcontroller without concern of driving

current into the pins of the external powered-down de-

vice.

To assure that the ÉlanSC310 microcontroller does not

draw excessive power while in this state, internal pull-

down resistors will be enabled. Enabling these resis-

tors keeps the input buffers from floating (see Figure 4).

On/Off

ACIN

ÉlanSC310

Microcontroller

RTC

PMU

Power Supply

Swapping

Circuit

Primary

Power

Supply

Secondary

Power Supply

IORESET

Main

Battery

3.3 V

5 V

Parallel/Serial

Power Management

Analog

ISA/LOCAL

ISA

ISA and Misc.

RESIN

VCC

(Core)

AVCC

Figure 3.

Typical System Design with Secondary Power Supply to Maintain RTC When

Primary Power Supply is Off (DRAM Refresh is Optional.)

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