pc87591l-n05 National Semiconductor Corporation, pc87591l-n05 Datasheet - Page 318

• Manufacturer Part Number: pc87591l-n05
• Description: Lpc Mobile Embedded Controller
• Manufacturer: National Semiconductor Corporation

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Host-Controlled Modules and Host Interface
6.2
The RTC provides timekeeping and calendar management capabilities. It uses a 32.768 KHz signal as the basic clock for
timekeeping. The RTC also includes 242 bytes of battery-backed RAM for general-purpose use.
The RTC provides the following functions:
6.2.1
The RTC function is initially mapped to the default SuperI/O locations at indexes 70
locations may be reassigned in compliance with Plug and Play requirements.
6.2.2
The RTC uses a 32.768 KHz clock signal as the basic clock for timekeeping. The 32.768 KHz clock is generated by the in-
ternal oscillator circuit or by an external oscillator (see Sections 6.2.3 and 6.2.4).
6.2.3
The internal oscillator employs an external crystal connected to the on-chip amplifier. The on-chip amplifier is accessible on
the 32KX1 input pin and the 32KX2 output pin. See Figure 105 for the recommended external circuit and Table 55 for a list-
ing of the circuit components. The oscillator may be disabled in certain conditions. See Section 6.2.12 on page 324 for more
details.
• Accurate timekeeping and calendar management
• Alarm at a predetermined time and/or date
• Three programmable interrupt sources
• Valid timekeeping during power-down, by utilizing external battery backup
• 242 bytes of battery-backed RAM
• RAM lock schemes to protect its content
• Internal oscillator circuit (the crystal itself is off-chip) or external clock supply for the 32.768 KHz clock
• A century counter
• PnP support:
• Additional low-power features such as:
• Software compatible with the DS1287 and MC146818
— Relocatable index and data registers
— Module access enable/disable option
— Host interrupt enable/disable option
— Automatic switching from battery to V
— Internal power monitoring on the VRT bit
REAL-TIME CLOCK (RTC)
Bus Interface
RTC Clock Generation
Internal Oscillator
Figure 105. Recommended Oscillator External Circuitry
Battery
V
BAT
B1
32KCLKIN
CF
32KX1 /
CC
C1
318
R
Y
1
(Continued)
R
2
32KX2
C2
To other
modules
CF = 0.1 F
External
Internal
16
to 73
16
(two Index/Data pairs). These
Revision 1.2