PIC18FXX20
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.
2.7
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
TABLE 2-3:
OSC Mode
OSC1 AND OSC2 PIN STATES IN SLEEP MODE
OSC1 Pin
OSC2 Pin
RC
Floating, external resistor should pull high
At logic low
RCIO
ECIO
EC
Floating, external resistor should pull high
Configured as PORTA, bit 6
Configured as PORTA, bit 6
At logic low
Floating
Floating
LP, XT, and HS
Feedback inverter disabled, at quiescent
Feedback inverter disabled, at quiescent
voltage level
voltage level
Note: See Table 3-1 in the “Reset” section, for time-outs due to SLEEP and MCLR Reset.
With the PLL enabled (HS/PLL Oscillator mode), the
2.8
Power-up Delays
time-out sequence following a Power-on Reset is differ-
ent from other Oscillator modes. The time-out
sequence is as follows: First, 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)
time-out to allow the PLL ample time to lock to the
incoming clock frequency.
Power up delays are controlled by two timers, so that
no external RESET circuitry is required for most appli-
cations. The delays ensure that the device is kept in
RESET until the device power supply and clock are sta-
ble. For additional information on RESET operation,
see the “Reset” section.
The first timer is the Power-up Timer (PWRT), which
optionally provides a fixed delay of 72 ms (nominal) 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.
DS39609A-page 28
Advance Information
2003 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
