DSPIC30F4012 Microchip Technology Inc., DSPIC30F4012 Datasheet - Page 155

• Manufacturer Part Number: DSPIC30F4012
• Description: Dspic30f4011/4012 Enhanced Flash 16-bit Digital Signal Controller
• Manufacturer: Microchip Technology Inc.

21.3.1.1
The oscillator start-up circuitry is not linked to the POR
circuitry.
frequency crystals) 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
• 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 occurs. The device
automatically switches to the FRC oscillator and the
user can switch to the desired crystal oscillator in the
trap ISR.
21.3.1.2
If the FSCM is disabled and the Power-up Timer
(PWRT) is also disabled, then the device exits rapidly
from Reset on power-up. If the clock source is FRC,
LPRC, ERC 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.
21.3.2
The BOR (Brown-out Reset) module is based on an
internal voltage reference circuit. The main purpose of
the BOR module is to generate a device Reset when a
brown-out condition occurs. Brown-out conditions are
generally caused by glitches on the AC mains (i.e.,
missing portions of the AC cycle waveform due to bad
power transmission lines, or voltage sags due to exces-
sive current draw when a large inductive load is turned
on).
The BOR module allows selection of one of the
following voltage trip points (see Table 24-10 ):
• 2.6V-2.71V
• 4.1V-4.4V
• 4.58V-4.73V
© 2007 Microchip Technology Inc.
crystal oscillator is used).
Note:
Some crystal
BOR: PROGRAMMABLE
BROWN-OUT RESET
The BOR voltage trip points indicated here
are nominal values provided for design
guidance only.
POR with Long Crystal Start-up Time
Operating without FSCM and PWRT
(with FSCM Enabled)
circuits (especially low-
A BOR generates a Reset pulse, which resets the
device. The BOR selects the clock source, based on
the device Configuration bit values (FOS<1:0> and
FPR<3:0>). Furthermore, if an oscillator mode is
selected, the BOR activates the Oscillator Start-up
Timer (OST). The system clock is held until OST
expires. If the PLL is used, then the clock is held until
the LOCK bit (OSCCON<5>) is ‘1’.
Concurrently, the POR time-out (T
time-out (T
is released. If T
being used, then a nominal delay of T
applied. The total delay in this case is (T
The BOR status bit (RCON<1>) is set to indicate that a
BOR has occurred. The BOR circuit, if enabled, contin-
ues to operate while in Sleep or Idle modes and resets
the device if V
FIGURE 21-6:
Note:
Note 1: External Power-on Reset circuit is required
dsPIC30F4011/4012
2: R should be suitably chosen so as to make
3: R1 should be suitably chosen so as to limit
PWRT
D
Dedicated supervisory devices, such as
the MCP1XX and MCP8XX, may also be
used as an external Power-on Reset
circuit.
only if the V
The diode D helps discharge the capacitor
quickly when V
sure that the voltage drop across R does not
violate the device’s electrical specification.
any current flowing into MCLR from external
capacitor C, in the event of MCLR pin break-
down, due to Electrostatic Discharge (ESD)
or Electrical Overstress (EOS).
DD
V
) are applied before the internal Reset
PWRT
falls below the BOR threshold voltage.
DD
R
C
EXTERNAL POWER-ON
RESET CIRCUIT (FOR
SLOW V
= 0 and a crystal oscillator is
DD
DD
R1
power-up slope is too slow.
powers down.
DD
MCLR
dsPIC30F
POR
DS70135E-page 153
POWER-UP)
FSCM
) and the PWRT
POR
= 100 μs is
+ T
FSCM
).