MCP795W22 datasheet(2/54 Pages) MICROCHIP

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MCP795W1X/MCP795W2X

DS22280C-page 2

Preliminary

 2011-2012 Microchip Technology Inc.

Description:

The MCP795WXX is a low-power Real-Time Clock/

Calendar (RTCC) that uses digital trimming compen-

sation for an accurate clock/calendar, an interrupt

output to support alarms and events, a power sense

circuit that automatically switches to the backup

supply, nonvolatile memory for safe data storage and

several enhanced features that support system

requirements.

Along with a low-cost 32,768 kHz crystal, this RTCC

tracks time using several internal registers and then

communicates the data over a 5 MHz SPI bus that is

fast enough to support a programmable millisecond

alarm.

The device is fully accessible through the serial

interface, while VCC is between 1.8V and 3.6V, but can

operate down to 1.3V through the backup supply

connected to the VBAT input for timekeeping and

SRAM retention only.

As part of the power sense circuit, a time saver

function is implemented to store the time when main

power is lost and again, when power is restored to log

the duration of a power failure.

Along with the on-board serial EEPROM and battery-

backed SRAM, a 128-bit protected space is available

for a unique ID. This space can be ordered

preprogrammed with a MAC address, or blank for the

user to program.

This clock/calendar automatically adjusts for months

with fewer than 31 days including corrections for leap

years. The clock operates in either 24-hour or 12-hour

format with AM/PM indicator and settable alarm(s).

Using the external crystal, the CLKOUT pin can be set

to generate a number of output frequencies.

For versatility, a digital event detect with a

programmable pulse count can identify the 1st, 4th,

16th or 32nd pulse before sending an interrupt. A

second event detect with built-in debounce input filter

was also implemented to support noisy mechanical

switches.

Since many microcontrollers do not have an integrated

Watchdog

Timer,

this

peripheral

has

been

implemented in the RTCC. For many applications, this

function must be performed outside the microcontroller

for increased robustness.

FIGURE 1-1:

BLOCK DIAGRAM

VBAT

IRQ

VSS

VCC

CLKOUT/

BOOT

EVHS

EVLS

SCK

SDI

SDO

OSC

CLKOUT Divider

WDT

SPI

EEPROM

SRAM

TIME-STAMP

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