PIC16F818/819
FIGURE 4-2:
CERAMIC RESONATOR
4.3
External Clock Input
OPERATION (HS OR XT
OSC CONFIGURATION)
The ECIO Oscillator mode requires an external clock
source to be connected to the OSC1 pin. There is no
oscillator start-up time required after a Power-on Reset
or after an exit from Sleep mode.
OSC1
PIC16F818/819
C1(1)
In the ECIO Oscillator mode, the OSC2 pin becomes
an additional general purpose I/O pin. The I/O pin
becomes bit 6 of PORTA (RA6). Figure 4-3 shows the
pin connections for the ECIO Oscillator mode.
RES
(3)
RF
Sleep
OSC2
(2)
RS
C2(1)
To Internal
Logic
FIGURE 4-3:
EXTERNAL CLOCK INPUT
OPERATION
Note 1: See Table 4-2 for typical values of C1 and C2.
2: A series resistor (RS) may be required.
(ECIO CONFIGURATION)
3: RF varies with the resonator chosen (typically
between 2 MΩ to 10 MΩ).
OSC1/CLKI
Clock from
Ext. System
PIC16F818/819
I/O (OSC2)
RA6
TABLE 4-2:
CERAMIC RESONATORS (FOR
DESIGN GUIDANCE ONLY)
Typical Capacitor Values Used:
Mode
Freq
OSC1
OSC2
XT
455 kHz
2.0 MHz
4.0 MHz
56 pF
47 pF
33 pF
56 pF
47 pF
33 pF
HS
8.0 MHz
16.0 MHz
27 pF
22 pF
27 pF
22 pF
Capacitor values are for design guidance only.
These capacitors were tested with the resonators
listed below for basic start-up and operation. These
values were not optimized.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
VDD and temperature range for the application.
See the notes following this table for additional
information.
Note:
When using resonators with frequencies
above 3.5 MHz, the use of HS mode rather
than XT mode is recommended. HS mode
may be used at any VDD for which the
controller is rated. If HS is selected, it is
possible that the gain of the oscillator will
overdrive the resonator. Therefore, a
series resistor should be placed between
the OSC2 pin and the resonator. As a
good starting point, the recommended
value of RS is 330Ω.
DS39598E-page 34
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
