MCP7940N-ESLASHMS datasheet(14/58 Pages) MICROCHIP

14 / 58 page

MCP7940N

DS20005010J-page 14

 2011-2022 Microchip Technology Inc. and its subsidiares

FIGURE 5-3:

SUGGESTED PLACEMENT OF THE OSCILLATOR CIRCUIT

5.2.2

EXTERNAL CLOCK INPUT

A 32.768 kHz external clock source can be connected

to the X1 pin (Figure 5-4). When using this

configuration, the X2 pin should be left floating.

FIGURE 5-4:

EXTERNAL CLOCK INPUT

OPERATION

5.2.3

OSCILLATOR FAILURE STATUS

The MCP7940N features an oscillator failure flag,

OSCRUN, that indicates whether or not the oscillator is

running. The OSCRUN bit is automatically set after 32

oscillator cycles are detected. If no oscillator cycles are

detected for more than TOSF, then the OSCRUN bit is

automatically cleared (Figure 5-5). This can occur if the

oscillator is stopped by clearing the ST bit or due to

oscillator failure.

FIGURE 5-5:

OSCILLATOR FAILURE STATUS TIMING DIAGRAM

TABLE 5-2:

SUMMARY OF REGISTERS ASSOCIATED WITH OSCILLATOR CONFIGURATION

GND

DEVICE PINS

CX1

CX2

GND

Bottom Layer

Copper Pour

Oscillator

Crystal

Top Layer Copper Pour

CX1

CX2

DEVICE PINS

(tied to ground)

Single-Sided and In-line Layouts:

Fine-Pitch (Dual-Sided) Layouts:

Oscillator

Crystal

Copper Pour

(tied to ground)

Note:

The EXTOSC bit must be set to enable an

external clock source.

Clock from

Ext. Source

MCP7940N

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

on Page

RTCSEC

SECTEN2 SECTEN1 SECTEN0

SECONE3

SECONE2 SECONE1 SECONE0

RTCWKDAY

—

OSCRUN

PWRFAIL

VBATEN

WKDAY2

WKDAY1

WKDAY0

CONTROL

OUT

SQWEN

ALM1EN

ALM0EN

EXTOSC

CRSTRIM

SQWFS1

SQWFS0

Legend:

— = unimplemented location, read as ‘0’. Shaded cells are not used by oscillator configuration.

OSCRUN Bit

< TOSF

TOSF

32 Clock Cycles

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