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

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Image 85
Emerson PMPPC7448 user manual Real-Time Clock, Block Diagram, Operation