Microchip Technology AC244055 Data Sheet
PIC16(L)F1938/9
DS40001574C-page 80
2011-2013 Microchip Technology Inc.
6.4
MCLR
The MCLR is an optional external input that can reset
the device. The MCLR function is controlled by the
MCLRE bit of Configuration Words and the LVP bit of
Configuration Words (
the device. The MCLR function is controlled by the
MCLRE bit of Configuration Words and the LVP bit of
Configuration Words (
).
6.4.1
MCLR ENABLED
When MCLR is enabled and the pin is held low, the
device is held in Reset. The MCLR pin is connected to
V
device is held in Reset. The MCLR pin is connected to
V
DD
through an internal weak pull-up.
The device has a noise filter in the MCLR Reset path.
The filter will detect and ignore small pulses.
The filter will detect and ignore small pulses.
6.4.2
MCLR DISABLED
When MCLR is disabled, the pin functions as a general
purpose input and the internal weak pull-up is under
software control. See
purpose input and the internal weak pull-up is under
software control. See
6.5
Watchdog Timer (WDT) Reset
The Watchdog Timer generates a Reset if the firmware
does not issue a CLRWDT instruction within the time-out
period. The TO and PD bits in the STATUS register are
changed to indicate the WDT Reset. See Section 10.0
“Watchdog Timer” for more information.
does not issue a CLRWDT instruction within the time-out
period. The TO and PD bits in the STATUS register are
changed to indicate the WDT Reset. See Section 10.0
“Watchdog Timer” for more information.
6.6
RESET Instruction
A RESET instruction will cause a device Reset. The RI
bit in the PCON register will be set to ‘0’. See
bit in the PCON register will be set to ‘0’. See
for default conditions after a RESET instruction has
occurred.
occurred.
6.7
Stack Overflow/Underflow Reset
The device can reset when the Stack Overflows or
Underflows. The STKOVF or STKUNF bits of the PCON
register indicate the Reset condition. These Resets are
enabled by setting the STVREN bit in Configuration
Words. See
Underflows. The STKOVF or STKUNF bits of the PCON
register indicate the Reset condition. These Resets are
enabled by setting the STVREN bit in Configuration
Words. See
for more information.
6.8
Programming Mode Exit
Upon exit of Programming mode, the device will
behave as if a POR had just occurred.
behave as if a POR had just occurred.
6.9
Power-Up Timer
The Power-up Timer optionally delays device execution
after a BOR or POR event. This timer is typically used to
allow V
after a BOR or POR event. This timer is typically used to
allow V
DD
to stabilize before allowing the device to start
running.
The Power-up Timer is controlled by the PWRTE bit of
Configuration Words.
The Power-up Timer is controlled by the PWRTE bit of
Configuration Words.
6.10
Start-up Sequence
Upon the release of a POR or BOR, the following must
occur before the device will begin executing:
1.
occur before the device will begin executing:
1.
Power-up Timer runs to completion (if enabled).
2.
Oscillator start-up timer runs to completion (if
required for oscillator source).
required for oscillator source).
3.
MCLR must be released (if enabled).
The total time-out will vary based on oscillator configu-
ration and Power-up Timer configuration. See
ration and Power-up Timer configuration. See
The Power-up Timer and oscillator start-up timer run
independently of MCLR Reset. If MCLR is kept low
long enough, the Power-up Timer and oscillator start-
up timer will expire. Upon bringing MCLR high, the
device will begin execution immediately (see
independently of MCLR Reset. If MCLR is kept low
long enough, the Power-up Timer and oscillator start-
up timer will expire. Upon bringing MCLR high, the
device will begin execution immediately (see
). This is useful for testing purposes or to synchronize
more than one device operating in parallel.
TABLE 6-2:
MCLR CONFIGURATION
MCLRE
LVP
MCLR
0
0
Disabled
1
0
Enabled
x
1
Enabled
Note:
A Reset does not drive the MCLR pin low.