41594B datasheet(92/372 Pages) MICROCHIP

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PIC12LF1840T48A

DS41594B-page 92

Preliminary

 2011-2012 Microchip Technology Inc.

10.1

Independent Clock Source

The WDT derives its time base from the 31 kHz

LFINTOSC internal oscillator.

10.2

WDT Operating Modes

The Watchdog Timer module has four operating modes

controlled by the WDTE<1:0> bits in Configuration

Word 1. See Table 10-1.

10.2.1

WDT IS ALWAYS ON

When the WDTE bits of Configuration Word 1 are set to

‘11’, the WDT is always on.

WDT protection is active during Sleep.

10.2.2

WDT IS OFF IN SLEEP

When the WDTE bits of Configuration Word 1 are set to

‘10’, the WDT is on, except in Sleep.

WDT protection is not active during Sleep.

10.2.3

WDT CONTROLLED BY SOFTWARE

When the WDTE bits of Configuration Word 1 are set to

‘01’, the WDT is controlled by the SWDTEN bit of the

WDTCON register.

WDT protection is unchanged by Sleep. See

Table 10-1 for more details.

TABLE 10-1:

WDT OPERATING MODES

10.3

Time-Out Period

The WDTPS bits of the WDTCON register set the

time-out period from 1ms to 256 seconds. After a

Reset, the default time-out period is two seconds.

10.4

Clearing the WDT

The WDT is cleared when any of the following condi-

tions occur:

•Any Reset

• CLRWDT instruction is executed

• Device enters Sleep

• Device wakes up from Sleep

• Oscillator fail event

• WDT is disabled

•OST is running

See Table 10-2 for more information.

10.5

Operation During Sleep

When the device enters Sleep, the WDT is cleared. If

the WDT is enabled during Sleep, the WDT resumes

counting.

When the device exits Sleep, the WDT is cleared

again. The WDT remains clear until the OST, if

enabled, completes. See Section 5.0 “Oscillator

Module (With Fail-Safe Clock Monitor)” for more

information on the OST.

When a WDT time-out occurs while the device is in

Sleep, no Reset is generated. Instead, the device

wakes up and resumes operation. The TO and PD bits

in the STATUS register are changed to indicate the

event. See Section 3.0 “Memory Organization” and

The

STATUS

(Register 3-1)

for

information.

WDTE

Config bits

SWDTEN

Device

Mode

WDT

Mode

WDT_ON (11)

XActive

WDT_NSLEEP (10)

Awake

Active

WDT_NSLEEP (10)

Sleep

Disabled

WDT_SWDTEN (01)

XActive

WDT_SWDTEN (01)

Disabled

WDT_OFF (00)

Disabled

TABLE 10-2:

WDT CLEARING CONDITIONS

Conditions

WDT

WDTE<1:0> = 00

Cleared

WDTE<1:0> = 01 and SWDTEN = 0

WDTE<1:0> = 10 and enter Sleep

CLRWDT Command

Oscillator Fail Detected

Exit Sleep + System Clock = T1OSC, EXTRC, INTOSC, EXTCLK

Exit Sleep + System Clock = XT, HS, LP

Cleared until the end of OST

Change INTOSC divider (IRCF bits)

Unaffected

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