PIC16F84A_07 Datasheet, PDF (25/88 Pages) Microchip Technology – 18-pin Enhanced FLASH/EEPROM 8-bit Microcontroller

TABLE 6-2: CAPACITOR SELECTION
FOR CRYSTAL OSCILLATOR
Mode
LP
XT
HS
Note:
Freq
OSC1/C1 OSC2/C2
32 kHz
200 kHz
100 kHz
2 MHz
4 MHz
68 - 100 pF
15 - 33 pF
100 - 150 pF
15 - 33 pF
15 - 33 pF
68 - 100 pF
15 - 33 pF
100 - 150 pF
15 - 33 pF
15 - 33 pF
4 MHz
20 MHz
15 - 33 pF
15 - 33 pF
15 - 33 pF
15 - 33 pF
Higher capacitance increases the stability
of the oscillator, but also increases the
start-up time. These values are for design
guidance only. Rs may be required in HS
mode, as well as XT mode, to avoid over-
driving crystals with low drive level specifi-
cation. Since each crystal has its own
characteristics, the user should consult the
crystal manufacturer for appropriate
values of external components.
For VDD > 4.5V, C1 = C2 ≈ 30 pF is recom-
mended.
PIC16F84A
6.2.3 RC OSCILLATOR
For timing insensitive applications, the RC device
option offers additional cost savings. The RC oscillator
frequency is a function of the supply voltage, the
resistor (REXT) values, capacitor (CEXT) values, and
the operating temperature. In addition to this, the oscil-
lator frequency will vary from unit to unit due to normal
process parameter variation. Furthermore, the
difference in lead frame capacitance between package
types also affects the oscillation frequency, especially
for low CEXT values. The user needs to take into
account variation, due to tolerance of the external
R and C components. Figure 6-3 shows how an R/C
combination is connected to the PIC16F84A.
FIGURE 6-3:
VDD
RC OSCILLATOR MODE
REXT
OSC1
Internal
Clock
CEXT
PIC16FXX
VSS
OSC2/CLKOUT
FOSC/4
Recommended values: 5 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20pF
© 2001 Microchip Technology Inc.
DS35007B-page 23