PIC24FJ256GB106-I Datasheet, PDF (67/328 Pages) Microchip Technology – 64/80/100-Pin, 16-Bit Flash Microcontrollers with USB On-The-Go (OTG)

PIC24FJ256GB110 FAMILY
5.2.1
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.
5.2.2
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.
5.2.2.1
FSCM Delay for Crystal and PLL
Clock Sources
When the system clock source is provided by a crystal
oscillator and/or the PLL, a small delay, TFSCM, will
automatically be inserted after the POR and PWRT
delay times. The FSCM will not begin to monitor the
system clock source until this delay expires. The FSCM
delay time is nominally 100 μs and provides additional
time for the oscillator and/or PLL to stabilize. In most
cases, the FSCM delay will prevent an oscillator failure
trap at a device Reset when the PWRT is disabled.
5.3 Special Function Register Reset
States
Most of the Special Function Registers (SFRs) associ-
ated with the PIC24F CPU and peripherals are reset to a
particular value at a device Reset. The SFRs are
grouped by their peripheral or CPU function and their
Reset values are specified in each section of this manual.
The Reset value for each SFR does not depend on the
type of Reset, with the exception of four registers. The
Reset value for the Reset Control register, RCON, will
depend on the type of device Reset. The Reset value
for the Oscillator Control register, OSCCON, will
depend on the type of Reset and the programmed
values of the FNOSC bits in Flash Configuration
Word 2 (CW2) (see Table 5-2). The RCFGCAL and
NVMCON registers are only affected by a POR.
© 2008 Microchip Technology Inc.
Preliminary
DS39897B-page 65