PC87570-ICCSLASHVUL datasheet(71/168 Pages) NSC

71 / 168 page

Real-Time Clock (RTC) and Advanced Power Control (APC)

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Bit 7 - Interrupt Request Flag (IRQF)

This read-only bit mirrors the value on the IRQ8 output

signal. When IRQ8 is active (low), IRQF is 1. The IRQ

pin is put in TRI-STATE while the host disables IRQ8

(IRQE.IRQ8E=0).

1: This bit is 1 if this logic equation is true:

(UIE and UF) or (AIE and AF) or (PIE and PF)= 1.

0: IRQ8 is inactive (high)

Note: To clear this bit (and deactivate the IRQ8 pin), read

the CRC Register as the ﬂag bits UF, AF and PF

are cleared after reading this register.

6.3.4

RTC Control Register D (CRD)

Bits 6-0 Reserved

These bits are always read 0.

Bit 7 - Valid RAM and Time (VRT)

This read-only bit is set to 1 when this register is read.

This bit must be read previously to enter power-down

mode, in order to keep the RTC oscillator enabled.

1: RTC register contents (time/calendar and CMOS

RAM) are valid

0: Battery source was too low or disconnected during

backup mode. Therefore, the RTC data and RAM

data are not valid. If this bit is 0, the RTC registers

cannot be written (see Section 6.3.1 on page 69).

This bit also affects the RTC oscillator activity (see Sec-

tion 6.2.15 on page 68).

6.4

USAGE HINTS

1. Read bit 7 of the CRD Register at each system power-

up to validate the contents of the RTC registers and the

CMOS RAM. When this bit is 0, the contents of these

registers and the CMOS RAM are questionable. This bit

is reset when the backup battery voltage is too low. The

voltage level at which this bit is reset is below the mini-

mum recommended battery voltage, 2.4 V. Although the

RTC oscillator may function properly and the register

contents may be correct at lower than 2.4 V, this bit is

reset since correct functionality cannot be guaranteed.

System BIOS may use a checksum method to revali-

date the contents of the CMOS-RAM. The checksum

byte should be stored in the same CMOS RAM.

2. Change the backup battery while normal operating pow-

er is present, and not in backup mode, to maintain valid

time and register information. If a low leakage capacitor

is connected to VBAT, the battery may be changed in

backup mode.

3. A rechargeable NiCd battery may be used instead of a

non-rechargeable Lithium battery. This is a preferred

solution for portable systems, where small size compo-

nents is essential.

4. A supercap capacitor may be used instead of the normal

Lithium battery. In a portable system usually the VCC

voltage is always present since the power management

stops the system before its voltage falls to low. The su-

percap capacitor in the range of 0.047-0.47 F should

supply the power during the battery replacement.

6.5

APC FUNCTIONAL DESCRIPTION

6.5.1

Operation

The APC enables the PC to power-up automatically under

various conditions, or to power-down in an orderly, con-

trolled manner. It can replace the physical power supply

On/Off switch.

The APC is powered from the VCC supply whenever VCC is

applied to the device. VCC is generated by a power supply

connected to the main battery. Partial operation is enabled

when a battery backup power (VBAT) is connected to the

RTC. This is true even though the PC may be switched off.

The APC may power-up the entire PC system in response

to various events. This ability makes it viable for use with

home PC applications such as PC-based fax machines,

modems and telephone answering machines, which previ-

ously required the PC to be powered up at all times.

The APC controls system power by generating the on re-

quest interrupt (APC-ON) and the off request interrupt

(APC-OFF) signals to the ICU through the MIWU.

The APC-OFF interrupt signal enables a software con-

trolled exit procedure (analogous to the DOS autoexec.bat

start-up procedure), with automatic activation of prepro-

grammed features, such as system status backup, system

activity logging, file closing and backup, remote communi-

cation termination, print completion, etc.

6.5.2

User Selectable Parameters

The APC enables you to tailor system response to power-

up, power-down and battery operation situations. User-se-

lectable parameters include:

Enabling external events to wake-up the system. See

"Power Up" on page 72.

Wake-up time for an automatic system wake-up. See

Section 6.5.7 on page 72.

6.5.3

System Power States

The valid system power states are listed in Table 6-5.

Table 6-5. Power States

No Power

This state exists when no VCC or VBAT is connected to the

device. The APC undergoes initialization only when leaving

this state.

Power Off

This state occurs when there is no VCC. The RTC continues

to maintain timekeeping and RAM data under VBAT unless

the oscillator in the RTC is disabled (see Table 6-4 on page

70). In this case, the oscillator stops functioning and time-

keeping data becomes invalid.

76543210

VRT

0000000

VCC

VBAT

Power State

−−

No Power

−

Power Off

++ or

−

Power On

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