PIC24FJ64GA705 Datasheet, PDF (84/412 Pages) –

PIC24FJ256GA705 FAMILY
7.4.1
POR AND LONG OSCILLATOR
START-UP TIMES
The oscillator start-up circuitry and its associated delay
timers are not linked to the device Reset delays that
occur at power-up. Some crystal circuits (especially low-
frequency crystals) will have a relatively long start-up
time. Therefore, one or more of the following conditions
is possible after SYSRST is released:
• The oscillator circuit has not begun to oscillate.
• The Oscillator Start-up Timer has not expired (if a
crystal oscillator is used).
• The PLL has not achieved a lock (if PLL is used).
The device will not begin to execute code until a valid
clock source has been released to the system. There-
fore, the oscillator and PLL start-up delays must be
considered when the Reset delay time must be known.
7.4.2
FAIL-SAFE CLOCK MONITOR
(FSCM) AND DEVICE RESETS
If the FSCM is enabled, it will begin to monitor the
system clock source when SYSRST is released. If a
valid clock source is not available at this time, the
device will automatically switch to the FRC Oscillator
and the user can switch to the desired crystal oscillator
in the Trap Service Routine (TSR).
DS30010118B-page 84
 2016 Microchip Technology Inc.