PIC18F6620 Microchip, PIC18F6620 Datasheet - Page 139

• Manufacturer Part Number: PIC18F6620
• Description: Microcontroller
• Manufacturer: Microchip

12.2
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 oscil-
lator is a low-power oscillator, rated up to 200 kHz. It
will continue to run during Sleep. It is primarily intended
for a 32 kHz crystal. The circuit for a typical LP oscilla-
tor is shown in Figure 12-3. Table 12-1 shows the
capacitor selection for the Timer1 oscillator.
The user must provide a software time delay to ensure
proper start-up of the Timer1 oscillator
FIGURE 12-3:
TABLE 12-1:
 2004 Microchip Technology Inc.
32.768 kHz Epson C-001R32.768K-A
Osc Type
Note 1: Microchip suggests 33 pF as a starting
Note:
LP
2: Higher capacitance increases the stability
3: Since each resonator/crystal has its own
4: Capacitor values are for design guidance
Timer1 Oscillator
33 pF
33 pF
C1
C2
See the Notes with Table 12-1 for additional
information about capacitor selection.
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.
Crystal to be Tested:
32 kHz
PIC18F6520/8520/6620/8620/6720/8720
Freq
CAPACITOR SELECTION
FOR THE ALTERNATE
OSCILLATOR
32.768 kHz
XTAL
EXTERNAL
COMPONENTS FOR THE
TIMER1 LP OSCILLATOR
values
TBD
T1OSI
T1OSO
C1
PIC18FXX20
(1)
of
TBD
20 PPM
external
C2
(1)
12.2.1
The Timer1 oscillator for PIC18LFX520 devices incor-
porates a low-power feature, which allows the oscillator
to automatically reduce its power consumption when
the microcontroller is in Sleep mode.
As high noise environments may cause excessive
oscillator instability in Sleep mode, this option is best
suited for low noise applications where power
conservation is an important design consideration. 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 12-3, 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 (such as the CCP1 pin in output compare or PWM
mode, or the primary oscillator using the OSC2 pin), a
grounded guard ring around the oscillator circuit, as
shown in Figure 12-4, may be helpful when used on a
single-sided PCB or in addition to a ground plane.
FIGURE 12-4:
Note:
Note:
LOW-POWER TIMER1 OPTION
(PIC18FX520 DEVICES ONLY)
PIC18FX620/X720
standard Timer1 oscillator permanently
selected.
have the low-power Timer1 oscillator
permanently selected.
Not drawn to scale.
OSCILLATOR CIRCUIT
WITH GROUNDED
GUARD RING
PIC18LFX620/X720
SS
OSC1
RC0
V
V
OSC2
RC1
RC2
devices
or V
DD
SS
DS39609B-page 137
DD
.
have
devices
the