PIC18F8527-I View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
PIC18F8527-I
Microchip Technology
PIC18F8527-I Datasheet PDF : 448 Pages
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PIC18F8722 FAMILY
4.4 Brown-out Reset (BOR)
The PIC18F8722 family of devices implements a BOR
circuit that provides the user with a number of con-
figuration and power-saving options. The BOR is con-
trolled by the BORV1:BORV0 and BOREN1:BOREN0
configuration bits. There are a total of four BOR
configurations which are summarized in Table 4-1.
The BOR threshold is set by the BORV1:BORV0 bits. If
BOR is enabled (any values of BOREN1:BOREN0,
except ‘00’), any drop of VDD below VBOR (parameter
D005, Section 28.1 “DC Characteristics”) for greater
than TBOR (parameter 35, Table 28-12) will reset the
device. A Reset may or may not occur if VDD falls below
VBOR for less than TBOR. The chip will remain in
Brown-out Reset until VDD rises above VBOR.
If the Power-up Timer is enabled, it will be invoked after
VDD rises above VBOR; it then will keep the chip in
Reset for an additional time delay, TPWRT
(parameter 33, Table 28-12). If VDD drops below VBOR
while the Power-up Timer is running, the chip will go
back into a Brown-out Reset and the Power-up Timer
will be initialized. Once VDD rises above VBOR, the
Power-up Timer will execute the additional time delay.
BOR and the Power-on Timer (PWRT) are
independently configured. Enabling BOR Reset does
not automatically enable the PWRT.
4.4.1 SOFTWARE ENABLED BOR
When BOREN1:BOREN0 = 01, the BOR can be
enabled or disabled by the user in software. This is
done with the control bit, SBOREN (RCON<6>).
Setting SBOREN enables the BOR to function as
previously described. Clearing SBOREN disables the
BOR entirely. The SBOREN bit operates only in this
mode; otherwise it is read as ‘0’.
Placing the BOR under software control gives the user
the additional flexibility of tailoring the application to its
environment without having to reprogram the device to
change the BOR configuration. It also allows the user
to tailor device power consumption in software by
eliminating the incremental current that the BOR con-
sumes. While the BOR current is typically very small, it
may have some impact in low-power applications.
Note:
Even when BOR is under software control,
the BOR Reset voltage level is still set by
the BORV1:BORV0 configuration bits. It
cannot be changed in software.
4.4.2 DETECTING BOR
When BOR is enabled, the BOR bit always resets to ‘0’
on any BOR or POR event. This makes it difficult to
determine if a BOR event has occurred just by reading
the state of BOR alone. A more reliable method is to
simultaneously check the state of both POR and BOR.
This assumes that the POR bit is reset to ‘1’ in software
immediately after any POR event. If BOR is ‘0’ while
POR is ‘1’, it can be reliably assumed that a BOR event
has occurred.
4.4.3 DISABLING BOR IN SLEEP MODE
When BOREN1:BOREN0 = 10, the BOR remains
under hardware control and operates as previously
described. Whenever the device enters Sleep mode,
however, the BOR is automatically disabled. When the
device returns to any other operating mode, BOR is
automatically re-enabled.
This mode allows for applications to recover from
brown-out situations, while actively executing code,
when the device requires BOR protection the most. At
the same time, it saves additional power in Sleep mode
by eliminating the small incremental BOR current.
TABLE 4-1: BOR CONFIGURATIONS
BOR Configuration
BOREN1 BOREN0
Status of
SBOREN
(RCON<6>)
BOR Operation
0
0
Unavailable BOR disabled; must be enabled by reprogramming the configuration bits.
0
1
Available BOR enabled in software; operation controlled by SBOREN.
1
0
Unavailable BOR enabled in hardware in Run and Idle modes, disabled during
Sleep mode.
1
1
Unavailable BOR enabled in hardware; must be disabled by reprogramming the
configuration bits.
DS39646B-page 52
Preliminary
2004 Microchip Technology Inc.
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