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10006757-02 PmPPC7448 User’s Manual
9-1
Section 9
Real-Time Clock
The standard real-time clock (RTC) for the PmPPC7448 is provided by an M41T00 device
from STMicroelectronics. This device has an integrated year-2000-compatible RTC, power
sense circuitry, and uses eight bytes of non-volatile RAM for the clock/calendar function.
The M41T00 is powered from the +3.3 volt rail during normal operation.
Caution: A supercapacitor on the PmPPC7448 provides backup operation in the event of a power
failure. However, if power is not reapplied within 12 hours, all data stored in non-volatile
RAM may be lost.
BLOCK DIAGRAM
Figure 9-1: M41T00 Real-Time Clock Block Diagram
OPERATION
The M41T00 clock operates as a slave device on the serial bus. To obtain access, the RTC
implements a start condition followed by the correct slave address (D0h). Access the eight
bytes in the following order:
!
Seconds
Minutes
Century/Hours
Day
Date
Month
Year
Control
1Hz
OSC1
OSC0
FT/OUT
SCL
SDA
V
CC
V
SS
V
BAT
Address
Register
Control
Logic
Divider
Oscillator
32.768 KHz
Voltage
Sense and
Switch
Circuitry
Serial
Bus
Interface