PC87570 Datasheet, PDF (71/168 Pages) National Semiconductor (TI) – PC87570 Keyboard and Power Management Controller

Real-Time Clock (RTC) and Advanced Power Control (APC)
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)
7
6
5
4
3
2
1
0
VRT 0
0
0
0
0
0
0
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 V_BAT, 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 V_CC
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 V_CC supply whenever V_CC is
applied to the device. V_CC is generated by a power supply
connected to the main battery. Partial operation is enabled
when a battery backup power (V_BAT) 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:
q _{Enabling external events to wake-up the system. See}
"Power Up" on page 72.
q _{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
V_CC
V_BAT
−
−
−
+
+
+ or −
Power State
No Power
Power Off
Power On
No Power
This state exists when no V_CC or V_BAT is connected to the
device. The APC undergoes initialization only when leaving
this state.
Power Off
This state occurs when there is no V_CC. The RTC continues
to maintain timekeeping and RAM data under V_BAT 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.
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