PIC16F84A_13 Datasheet, PDF (22/90 Pages) Microchip Technology – 18-pin Enhanced FLASH/EEPROM 8-Bit Microcontroller

PIC16F84A
6.2 Oscillator Configurations
6.2.1
OSCILLATOR TYPES
The PIC16F84A can be operated in four different
oscillator modes. The user can program two
configuration bits (FOSC1 and FOSC0) to select one of
these four modes:
• LP
• XT
• HS
• RC
Low Power Crystal
Crystal/Resonator
High Speed Crystal/Resonator
Resistor/Capacitor
6.2.2
CRYSTAL OSCILLATOR/CERAMIC
RESONATORS
In XT, LP, or HS modes, a crystal or ceramic resonator
is connected to the OSC1/CLKIN and OSC2/CLKOUT
pins to establish oscillation (Figure 6-1).
FIGURE 6-1:
CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS, XT OR LP OSC
CONFIGURATION)
C1⁽¹⁾
OSC1
XTAL
OSC2
RS⁽²⁾
C2⁽¹⁾
RF⁽³⁾
To
Internal
Logic
SLEEP
PIC16FXX
Note 1: See Table 6-1 for recommended values
of C1 and C2.
2: A series resistor (RS) may be required
for AT strip cut crystals.
The PIC16F84A oscillator design requires the use of a
parallel cut crystal. Use of a series cut crystal may give
a frequency out of the crystal manufacturers
specifications. When in XT, LP, or HS modes, the
device can have an external clock source to drive the
OSC1/CLKIN pin (Figure 6-2).
FIGURE 6-2:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSC
CONFIGURATION)
Clock from
Ext. System
Open
OSC1
PIC16FXX
OSC2
TABLE 6-1: CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Ranges Tested:
Mode
Freq
OSC1/C1 OSC2/C2
XT
HS
Note:
455 kHz
2.0 MHz
4.0 MHz
47 - 100 pF 47 - 100 pF
15 - 33 pF 15 - 33 pF
15 - 33 pF 15 - 33 pF
8.0 MHz 15 - 33 pF 15 - 33 pF
10.0 MHz 15 - 33 pF 15 - 33 pF
Recommended values of C1 and C2 are
identical to the ranges tested in this table.
Higher capacitance increases the stability
of the oscillator, but also increases the
start-up time. These values are for design
guidance only. Since each resonator has
its own characteristics, the user should
consult the resonator manufacturer for the
appropriate values of external compo-
nents.
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.
DS35007C-page 22
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