Datasheet

dsPIC30F1010/202X
DS70178C-page 212 Preliminary © 2006 Microchip Technology Inc.
FIGURE 18-10: TIME-OUT SEQUENCE ON POWER-UP (MCLR NOT TIED TO VDD): CASE 2
18.7.1.1 POR with Long Crystal Start-up Time
(with FSCM Enabled)
The oscillator start-up circuitry is not linked to the POR
circuitry. 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 the POR timer and the PWRT have
expired:
• 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).
If the FSCM is enabled and one of the above conditions
is true, then a clock failure trap will occur. The device
will automatically switch to the FRC oscillator and the
user can switch to the desired crystal oscillator in the
trap, ISR.
18.7.1.2 Operating without FSCM and PWRT
If the FSCM is disabled and the Power-up Timer
(PWRT) is also disabled, then the device will exit rap-
idly from Reset on power-up. If the clock source is FRC
or EC, it will be active immediately.
If the FSCM is disabled and the system clock has not
started, the device will be in a frozen state at the Reset
vector until the system clock starts. From the user’s
perspective, the device will appear to be in Reset until
a system clock is available.
FIGURE 18-11: EXTERNAL POWER-ON
RESET CIRCUIT (FOR
SLOW V
DD POWER-UP)
VDD
MCLR
Internal POR
PWRT Time-out
OST Time-out
Internal Reset
TPWRT
TOST
Note: Dedicated supervisory devices, such as
the MCP1XX and MCP8XX, may also be
used as an external Power-on Reset
circuit.
Note 1: External Power-on Reset circuit is
required only if the V
DD power-up slope
is too slow. The diode D helps discharge
the capacitor quickly when V
DD powers
down.
2: R should be suitably chosen so as to
make sure that the voltage drop across
R does not violate the device’s electrical
specification.
3: R1 should be suitably chosen so as to
limit any current flowing into MCLR
from
external capacitor C, in the event of
MCLR/VPP pin breakdown due to Elec-
trostatic Discharge (ESD) or Electrical
Overstress (EOS).
C
R1
R
D
V
DD
dsPIC30F
MCLR