PC87307VUL National Semiconductor, PC87307VUL Datasheet - Page 51

• Manufacturer Part Number: PC87307VUL
• Description: PC87307/PC97307 Plug and Play Compatible and PC97 Compliant SuperI/O
• Manufacturer: National Semiconductor

Alarms
The timekeeping function may generate an alarm when the
current time reaches a stored alarm time. After each RTC
time update, the seconds, minutes, and hours storage loca-
tions are compared with the seconds, minutes and hours in
the alarm storage locations. If equal, the alarm flag is set in
Control Register C (CRC). If the Alarm Interrupt Enable
(AIE) bit is set in Control Register B (CRB), then setting the
Alarm Flag (AF) in CRC generates the IRQ internal interrupt
request (IRQ = 0).
Any alarm location, i.e., seconds, minutes or hours, may be
set to a “Don’t Care” state by setting bits 7,6 to 11. (This val-
ue is unused for either BCD or binary time codes.) This re-
sults in periodic alarm activation at an increased rate whose
period is that of the Don’t Care location, e.g., if the hours lo-
cation is set to 11, the alarm will be activated every hour.
The seconds, minutes and hours alarm registers are shared
with the wake-up function.
Modules
PC87307/
PC97307
RTC
APC
and
Host PC
Real-Time Clock (RTC) and Advanced Power Control (APC) (Logical Device 2)
FIGURE 4-2. PC87307/PC97307 Power Supplies
V
CCH
FIGURE 4-3. Typical Battery Configuration
V
V
V
V
DD
CCH
BAT
DD
ONCTL
Sense
Power
Power
Power
1
0.1
F
F
51
V
V
CCH
Power Supply Module
BAT
4.1.3
The host PC and part power is supplied by the system pow-
er supply voltage, V
Figure 4-2 shows the power supplies of the part.
A stand-by voltage (V
ply powers the RTC and APC under normal conditions. The
V
termine the presence or absence of a valid V
A battery backup voltage V
keeping and backup memory storage when the V
age is absent, due to power failure or disconnection of the
external AC input power supply.
The APC function produces the ONCTL signal, which con-
trols the V
page 58.)
To ensure proper operation, a 500 mV differential is needed
between V
Figure 4-3 represents a typical battery configuration. No ex-
ternal diode is required to meet the UL standard, due to the
internal serial resistor.
DD
PC87307/
voltage reaches the RTC/APC as a sense signal, to de-
PC97307
Backup
Battery
Power Supply
V
V
DD
CCH
DD
CCH
power supply voltage. (See Section 4.4.1 on
and V
DD.
BAT
CCH
.
) from the external AC power sup-
BAT
External AC Power
maintains RTC/APC time-
DD
www.national.com
supply.
CCH
volt-