CS5535 datasheet(144/555 Pages) NSC

144 / 555 page

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144

Revision 0.8

4.14 REAL-TIME CLOCK FEATURES

The Real-Time Clock (RTC) consists of three main blocks:

the digital section, the analog section, and the level-shifter

block (see Figure 4-47). The digital section contains the

bus interface, RAM, voltage control, time generator, and

the time keeper. The analog section contains the voltage

switch and low power crystal oscillator. Finally, the level

shifter block provides the appropriate voltage level transla-

tion of signals to and from the RTC block. Level shifters are

needed because the RTC is powered by the VPP (output of

the analog section), which is different from the VCORE and

VCORE_VSB power domains.

Features

• Accurate timekeeping and calendar management

• Alarm at a predetermined time and/or date

• Three programmable interrupt sources

• Valid timekeeping during power-down, by utilizing

external battery backup

• 242 bytes of battery-backed RAM

• RAM lock schemes to protect its content

• Internal oscillator circuit (the crystal itself is off-chip), or

external clock supply for the 32.768 kHz clock

• A century counter

• Additional low-power features such as:

— Automatic switching from battery to VSB

— Internal power monitoring on the VRT bit

— Oscillator disabling to save battery during storage

• Software compatible with the DS1287 and MC146818

Figure 4-47. RTC Block Diagram

rtc_seconds

rtc_minutes

rtc_hours

rtc_monthday

rtc_months

rtc_years

Time Keeper

Index_Reg

Ctrl_Reg A, B, C, D

RAM I/F

Gated Clocks

Bus Interface

Time Generator

Update

242x8 Bit RAM

Voltage Control

Voltage Switch

Low Power Osc.

32 kHz Clock

VPP

VIO_VSB

VBAT

KHZ32_XCI

Write

Index

Read

Local Bus

Data & Ctrls

#14

KHZ32_XCO

Level Shifter

rtc_weekday

Data

Clock

Voltage

Sense

Voltage

Select

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