Datasheet

PIC16(L)F720/721
DS40001430E-page 96  2010-2013 Microchip Technology Inc.
13.5.2.1 T1G Pin Gate Operation
The T1G pin is one source for Timer1 gate control. It
can be used to supply an external source to the Timer1
gate circuitry.
13.5.2.2 Timer0 Overflow Gate Operation
When Timer0 increments from FFh to 00h, a low-to-
high pulse will automatically be generated and
internally supplied to the Timer1 gate circuitry.
13.5.2.3 Timer2 Match Gate Operation
The TMR2 register will increment until it matches the
value in the PR2 register. On the very next increment
cycle, TMR2 will be reset to 00h. When this Reset
occurs, a low-to-high pulse will automatically be
generated and internally supplied to the Timer1 gate
circuitry.
13.5.2.4 Watchdog Overflow Gate Operation
The Watchdog Timer oscillator, prescaler and counter
will be automatically turned on when TMR1GE = 1 and
T1GSS selects the WDT as a gate source for Timer1
(T1GSS = 11). TMR1ON does not factor into the oscil-
lator, prescaler and counter enable. See Table 13-5.
The PSA and PS bits of the OPTION_REG register still
control what time-out interval is selected. Changing the
prescaler during operation may result in a spurious
capture.
Enabling the Watchdog Timer oscillator does not
automatically enable a Watchdog Reset or Wake-up
from Sleep upon counter overflow.
As the gate signal coming from the WDT counter will
generate different pulse widths depending on if the
WDT is enabled, when the CLRWDT instruction is
executed, and so on, Toggle mode must be used. A
specific sequence is required to put the device into the
correct state to capture the next WDT counter interval.
Note: When using the WDT as a gate source for
Timer1, operations that clear the Watchdog
Timer (CLRWDT, SLEEP instructions) will
affect the time interval being measured.
This includes waking from Sleep. All other
interrupts that might wake the device from
Sleep should be disabled to prevent them
from disturbing the measurement period.
TABLE 13-5: WDT/TIMER1 GATE INTERACTION
WDTEN
TMR1GE = 1
and
T1GSS = 11
WDT Oscillator
Enable
WDT Reset Wake-up
WDT Available for
T1G Source
1
N
YYY N
1
Y
YYY Y
0
Y
YNN Y
0
N
NNN N