PIC18F23K20 Datasheet, PDF (54/420 Pages) Microchip Technology – 28/40/44-Pin Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology

PIC18F2XK20/4XK20
4.4 Brown-out Reset (BOR)
PIC18F2XK20/4XK20 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> bits of the
CONFIG2L Configuration register. There are a total of
four BOR configurations which are summarized in
Table 4-1.
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 VDD below VBOR (parameter D005)
for greater than TBOR (parameter 35) 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). 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 BOREN<1:0> = 01, the BOR can be enabled or
disabled by the user in software. This is done with the
SBOREN control bit of the RCON register. 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 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.
Note:
Even when BOR is under software control,
the BOR Reset voltage level is still set by
the BORV<1:0> Configuration bits. It can-
not be changed by 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 and BOR bits are reset to
‘1’ by 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 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 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 by software; operation controlled by SBOREN.
1
0
Unavailable BOR enabled by hardware in Run and Idle modes, disabled during
Sleep mode.
1
1
Unavailable BOR enabled by hardware; must be disabled by reprogramming the
Configuration bits.
DS41303B-page 52
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© 2007 Microchip Technology Inc.