MCP79411 datasheet(21/60 Pages) MICROCHIP

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DS20002266E-page 21

MCP79410/MCP79411/MCP79412

8.0

SPECIAL FEATURES

8.1

Oscillator Failure Status

The MCP7941X family of devices support an on-board

oscillator failure flag. In register 0x03 (Day Register –

shown below), the OSCON (bit 5) provides a way to

observe the current status of the oscillator.

The state of the bit indicates the oscillator status.

1 = The oscillator is running

0 = The oscillator is not running

The status does not indicate that the oscillator is run-

ning accurately. The OSCON bit is set after 32 stable

oscillator cycles. If the oscillator is stopped by either

clearing the ST bit or the oscillator support components

fail, the OSCON bit is cleared by the hardware after

TOSF. This is timed internally using an on-chip time-out

circuit.

Figure 8-1 shows the operation.

It should be noted that this bit is both set and cleared

by the RTCC hardware, and it will not show that the

oscillator failed in the past. The user can poll this bit at

any time to determine if the oscillator is running.

FIGURE 8-1:

OSCON DIAGRAM

OSCON Bit

(Register 0x03 Bit 5)

32 Oscillator Cycles

TOSF

Crystal Oscillator

<TOSF

DAY 0X03

U-0

R-0

R/W-0

R/W-1

—

OSCON

VBAT

VBATEN

Day

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

“0” = Bit is clear

“X” = Bit is unknown

bit 7-6

Unimplemented: Read as ‘0’

bit 5

OSCON: Oscillator Status bit

This bit is set and cleared by hardware.

1 = The external oscillator is enabled and running

0 = The external oscillator has stopped or has been disabled

bit 4

VBAT: External Battery Switched Flag bit.

Not used in this section.

bit 3

VBATEN: External Battery Enable bit

Not used in this section.

bit 2-0

DAY<2:0>: Not used in this section.

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