PIC18F258T-I/SOG【PDF 26/116 页】IC MCU FLASH 16KX16 28SOIC

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2006 Microchip Technology Inc.

DS41159E-page 23

PIC18FXX8

2.7

Effects of Sleep Mode on the

On-Chip Oscillator

When the device executes a SLEEP instruction, the

on-chip clocks and oscillator are turned off and the

device is held at the beginning of an instruction cycle

(Q1 state). With the oscillator off, the OSC1 and OSC2

signals will stop oscillating. Since all the transistor

switching currents have been removed, Sleep mode

achieves the lowest current consumption of the device

(only leakage currents). Enabling any on-chip feature

that will operate during Sleep will increase the current

consumed during Sleep. The user can wake from

Sleep through external Reset, Watchdog Timer Reset

or through an interrupt.

2.8

Power-up Delays

Power-up delays are controlled by two timers so that no

external Reset circuitry is required for most applica-

tions. The delays ensure that the device is kept in

Reset until the device power supply and clock are

stable. For additional information on Reset operation,

see Section 3.0 “Reset”.

The first timer is the Power-up Timer (PWRT), which

optionally provides a fixed delay of TPWRT (parameter

#D033) on power-up only (POR and BOR). The second

timer is the Oscillator Start-up Timer (OST), intended to

keep the chip in Reset until the crystal oscillator is

stable.

With the PLL enabled (HS4 Oscillator mode), the time-

out sequence following a Power-on Reset is different

from other oscillator modes. The time-out sequence is

as follows: the PWRT time-out is invoked after a POR

time delay has expired, then the Oscillator Start-up

Timer (OST) is invoked. However, this is still not a

sufficient amount of time to allow the PLL to lock at high

frequencies. The PWRT timer is used to provide an

additional fixed 2 ms (nominal) to allow the PLL ample

time to lock to the incoming clock frequency.

TABLE 2-3:

OSC1 AND OSC2 PIN STATES IN SLEEP MODE

OSC Mode

OSC1 Pin

OSC2 Pin

Floating, external resistor should pull high

At logic low

RCIO

Floating, external resistor should pull high

Configured as PORTA, bit 6

ECIO

Floating

Configured as PORTA, bit 6

Floating

At logic low

LP, XT and HS

Feedback inverter disabled at quiescent

voltage level

Feedback inverter disabled at quiescent

voltage level

Note:

See Table 3-1 in Section 3.0 “Reset” for time-outs due to Sleep and MCLR Reset.

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