MCP79400_13 datasheet(18/42 Pages) MICROCHIP

Part #	MCP79400

Description	I2C Real-Time Clock/Calendar with SRAM, Unique IDand Battery Switchover

PDF	42 Pages

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Manufacturer	MICROCHIP [Microchip Technology]

Direct Link	http://www.microchip.com

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18 / 42 page

MCP7940X

DS25009C-page 18

 2011 Microchip Technology Inc.

5.2.6

POWER-FAIL TIME-STAMP

The MCP7941X family of RTCC devices feature a

power-fail time-stamp feature. This feature will store

the time at which VCC crosses the VTRIP voltage and is

shown in Figure 5-4. To use this feature, a VBAT

supply must be present and the oscillator must also be

running.

There are two separate sets of registers that are used

to record this information:

• The first set, located at 0x18h through 0x1Bh, is

loaded at the time when VCC falls below VTRIP

and the RTCC operates on the VBAT. The VBAT

(register 0x03h bit 4) bit is also set at this time.

• The second set of registers, located at 0x1Ch

through 0x1Fh, is loaded at the time when VCC is

restored and the RTCC switches to VCC.

The power-fail time-stamp registers are cleared when

the VBAT bit is cleared in software.

FIGURE 5-4:

POWER-FAIL GRAPH

VCC

VTRIP(max)

VTRIP(min)

Power-Down

Power-Up

Time-Stamp

MCP79400 Datasheet(PDF) 18 Page - Microchip Technology