Datasheet

PIC18F6310/6410/8310/8410
DS39635C-page 58  2010 Microchip Technology Inc.
5.4 Brown-out Reset (BOR)
PIC18F6310/6410/8310/8410 devices implement a
BOR circuit that provides the user with a number of
configuration and power-saving options. The BOR is
controlled by the BORV<1:0> and BOREN<1:0>
Configuration bits. There are a total of four BOR
configurations, which are summarized in Ta b l e 5- 1 .
The BOR threshold is set by the BORV<1:0> bits. If BOR
is enabled (any values of BOREN<1:0> except ‘00’),
any drop of V
DD below VBOR (Parameter D005) for
greater than T
BOR (Parameter 35) will reset the device.
A Reset may or may not occur if V
DD falls below VBOR
for less than TBOR. The chip will remain in Brown-out
Reset until V
DD rises above VBOR.
If the Power-up Timer is enabled, it will be invoked after
V
DD rises above VBOR; it then will keep the chip in
Reset for an additional time delay, T
PWRT
(Parameter 33). 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 V
DD rises above VBOR, the Power-up
Timer will execute the additional time delay.
BOR and the Power-up Timer (PWRT) are
independently configured. Enabling the Brown-out
Reset does not automatically enable the PWRT.
5.4.1 SOFTWARE ENABLED BOR
When BOREN<1:0> = 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
consumes. While the BOR current is typically very
small, it may have some impact in low-power
applications.
5.4.2 DETECTING BOR
When Brown-out Reset is enabled, the BOR bit always
resets to ‘0’ on any BOR or POR event. This makes it
difficult to determine if a Brown-out Reset 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.
5.4.3 DISABLING BOR IN SLEEP MODE
When BOREN<1:0> = 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 5-1: BOR CONFIGURATIONS
Note: Even when BOR is under software con-
trol, the Brown-out Reset voltage level is
still set by the BORV<1:0> Configuration
bits. It cannot be changed in software.
BOR Configuration Status of
SBOREN
(RCON<6>)
BOR Operation
BOREN1 BOREN0
00Unavailable BOR is disabled; must be enabled by reprogramming the Configuration bits.
01Available BOR is enabled in software; operation controlled by SBOREN.
10Unavailable BOR is enabled in hardware and active during the Run and Idle modes;
disabled during Sleep mode.
11Unavailable BOR is enabled in hardware; must be disabled by reprogramming the
Configuration bits.