PIC16F819 Microchip Technology Inc., PIC16F819 Datasheet - Page 62

• Manufacturer Part Number: PIC16F819
• Description: 18/20-pin Enhanced Flash Microcontrollers With Nanowatt Technology
• Manufacturer: Microchip Technology Inc.

PIC16F818/819
7.6
A crystal oscillator circuit is built-in between pins T1OSI
(input) and T1OSO (amplifier output). It is enabled by
setting control bit, T1OSCEN (T1CON<3>). The
oscillator is a low-power oscillator, rated up to
32.768 kHz. It will continue to run during Sleep. It is
primarily intended for a 32 kHz crystal. The circuit for a
typical LP oscillator is shown in Figure 7-3. Table 7-1
shows the capacitor selection for the Timer1 oscillator.
The user must provide a software time delay to ensure
proper oscillator start-up.
FIGURE 7-3:
DS39598E-page 60
Note:
Note:
33 pF
33 pF
C2
C1
Timer1 Oscillator
The Timer1 oscillator shares the T1OSI
and T1OSO pins with the PGD and PGC
pins
debugging.
When using the Timer1 oscillator, In-Circuit
Serial Programming™ (ICSP™) may not
function correctly (high-voltage or low-
voltage) or the In-Circuit Debugger (ICD)
may not communicate with the controller.
As a result of using either ICSP or ICD, the
Timer1 crystal may be damaged.
If ICSP or ICD operations are required, the
crystal should be disconnected from the
circuit (disconnect either lead) or installed
after programming. The oscillator loading
capacitors may remain in-circuit during
ICSP or ICD operation.
See the Notes with Table 7-1 for additional
information about capacitor selection.
32.768 kHz
XTAL
used
EXTERNAL
COMPONENTS FOR THE
TIMER1 LP OSCILLATOR
for
T1OSI
T1OSO
PIC16F818/819
programming
and
TABLE 7-1:
7.7
The Timer1 oscillator circuit draws very little power
during operation. Due to the low-power nature of the
oscillator, it may also be sensitive to rapidly changing
signals in close proximity.
The oscillator circuit, shown in Figure 7-3, should be
located as close as possible to the microcontroller.
There should be no circuits passing within the oscillator
circuit boundaries other than V
If a high-speed circuit must be located near the oscilla-
tor, a grounded guard ring around the oscillator circuit,
as shown in Figure 7-4, may be helpful when used on
a single-sided PCB or in addition to a ground plane.
FIGURE 7-4:
Osc Type
Note 1: Microchip suggests this value as a starting
LP
2: Higher capacitance increases the stability
3: Since each resonator/crystal has its own
4: Capacitor values are for design guidance
Timer1 Oscillator Layout
Considerations
point in validating the oscillator circuit.
of the oscillator but also increases the
start-up time.
characteristics, the user should consult
the resonator/crystal manufacturer for
appropriate
components.
only.
32 kHz
Freq
CAPACITOR SELECTION FOR
THE TIMER1 OSCILLATOR
OSCILLATOR CIRCUIT
WITH GROUNDED
GUARD RING
 2004 Microchip Technology Inc.
values
SS
33 pF
C1
OSC1
V
OSC2
RB7
RB6
RB5
or V
SS
DD
of
.
33 pF
external
C2