Emerson PMPPC7448 사용자 설명서
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.
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.
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:
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
VCC
VSS
VBAT
Address
Register
Control
Logic
Divider
Oscillator
32.768 KHz
Voltage
Sense and
Switch
Circuitry
Serial
Bus
Interface