Emerson PMPPC7448 user manual Real-Time Clock, Block Diagram, Operation

Section 9

Real-Time Clock

Caution:

!

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.

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

OSC1	Oscillator	Divider	1Hz
			Seconds
OSC0	32.768 KHz
FT/OUT			Minutes
VCC	Voltage		Century/Hours
		Control
VSS	Sense and
		Logic	Day
	Switch
VBAT	Circuitry
			Date
			Month
SCL	Serial
	Bus		Year
	Interface
SDA
		Address
		Register	Control

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:

10006757-02 PmPPC7448 User’s Manual

9-1