SC2200 NSC [National Semiconductor], SC2200 Datasheet - Page 114

• Manufacturer Part Number: SC2200
• Description: Thin Client On a Chip
• Manufacturer: NSC [National Semiconductor]

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SuperI/O Module
4.5
The RTC provides timekeeping and calendar management
capabilities. The RTC uses a 32.768 KHz signal as the
basic clock for timekeeping. It also includes 242 bytes of
battery-backed RAM for general-purpose use.
The RTC provides the following functions:
• Accurate timekeeping and calendar management
• Alarm at a predetermined time and/or date
• Three programmable interrupt sources
• Valid timekeeping during power-down, by utilizing
• 242 bytes of battery-backed RAM
• RAM lock schemes to protect its content
• Internal oscillator circuit (the crystal itself is off-chip), or
• A century counter
• PnP support:
• Additional low-power features such as:
• Software compatible with the DS1287 and MC146818
4.5.1
The RTC function is initially mapped to the default SuperI/O
locations at Indexes 70h to 73h (two Index/Data pairs).
These locations may be reassigned, in compliance with
Plug and Play requirements.
Component
Crystal
Resistor R
Resistor R
Capacitor C
Capacitor C
external battery backup
external clock supply for the 32.768 KHz clock
— 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
— Oscillator disabling to save battery during storage
REAL-TIME CLOCK (RTC)
Bus Interface
1
2
1
2
Parameters
Resonance Frequency
Type
Serial Resistance
Quality Factor, Q
Shunt Capacitance
Load Capacitance, C
Temperature Coefficient
Resistance
Resistance
Capacitance
Capacitance
(Continued)
Table 4-17. Crystal Oscillator Circuit Components
SB
L
114
32.768 KHz Parallel mode
Values
N-cut or XY-bar
40 K
35000
2 pF
9-13 pF
User-defined
20 M
120 K
3 to 10 pF
3 to 10 pF
4.5.2
The RTC uses a 32.768 KHz clock signal as the basic
clock for timekeeping. The 32.768 KHz clock can be sup-
plied by the internal oscillator circuit, or by an external
oscillator (see Section 4.5.2.2 "External Oscillator" on page
115).
4.5.2.1
The internal oscillator employs an external crystal con-
nected to the on-chip amplifier. The on-chip amplifier is
accessible on the X32I input and X32O output. See Figure
4-5 for the recommended external circuit and Table 4-17 for
a listing of the circuit components. The oscillator may be
disabled in certain conditions. See Section 4.5.2.8 "Oscilla-
tor Activity" on page 118" for more details.
Figure 4-5. Recommended Oscillator External
Battery
V
RTC Clock Generation
BAT
B
C
1
Internal Oscillator
F
X32I
C
Circuitry
1
R
Y
1
R
Tolerance
User-defined
Max
Min
Max
5%
5%
5%
5%
2
X32O
C
2
To other
modules
C
External
F
Internal
= 0.1 F
Revision 3.0