RFPIC12C509AF datasheet(55/104 Pages) MICROCHIP

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Preliminary

DS70031A-page 53

rfPIC12C509AG/509AF

8.8

Power-Down Mode (SLEEP)

The SLEEP mode is designed to offer a very low cur-

rent power-down mode. The user can wake-up from

SLEEP through a change on input pins or through a

Watchdog Timer time-out. Several oscillator options

are also made available to allow the part to fit the appli-

cation, including an internal 4 MHz oscillator. The

EXTRC oscillator option saves system cost while the

LP crystal option saves power. A set of configuration

bits are used to select various options.

A device may be powered down (SLEEP) and later

powered up (Wake-up from SLEEP).

8.8.1

SLEEP

The Power-down mode is entered by executing a

SLEEP

instruction.

If enabled, the Watchdog Timer will be cleared but

keeps running, the TO bit (STATUS<4>) is set, the PD

bit (STATUS<3>) is cleared and the oscillator driver is

turned off. The I/O ports maintain the status they had

before the SLEEP instruction was executed (driving

high, driving low, or hi-impedance).

It should be noted that a RESET generated by a WDT

time-out does not drive the MCLR pin low.

For lowest current consumption while powered down,

the T0CKI input should be at VDD or VSS and the GP3/

MCLR/VPP pin must be at a logic high level (VIHMC)if

MCLR is enabled.

8.8.2

WAKE-UP FROM SLEEP

The device can wake-up from SLEEP through one of

the following events:

An external RESET input on GP3/MCLR/VPP

pin, when configured as MCLR.

A Watchdog Timer time-out Reset (if WDT was

enabled).

A change on input pin GP0, GP1, or GP3/

MCLR/VPP

when

wake-up

change

enabled.

These events cause a device RESET. The TO,PD,and

GPWUF bits can be used to determine the cause of

device RESET. The TO bit is cleared if a WDT time-out

occurred (and caused wake-up). The PD bit, which is

set on power-up, is cleared when SLEEP is invoked.

The GPWUF bit indicates a change in state while in

SLEEP at pins GP0, GP1, or GP3 (since the last time

there was a file or bit operation on GP port).

The WDT is cleared when the device wakes from

sleep, regardless of the wake-up source.

Caution:

Right before entering SLEEP, read the

input pins. When in SLEEP, wake up

occurs when the values at the pins change

from the state they were in at the last read-

ing. If a wake-up on change occurs and

the pins are not read before reentering

SLEEP, a wake up will occur immediately

even if no pins change while in SLEEP

mode.

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