Datasheet

 2001-2013 Microchip Technology Inc. DS35007C-page 23
PIC16F84A
TABLE 6-2: CAPACITOR SELECTION
FOR CRYSTAL OSCILLATOR
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 (R
EXT) 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 C
EXT 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: RC OSCILLATOR MODE
Mode Freq OSC1/C1 OSC2/C2
LP 32 kHz
200 kHz
68 - 100 pF
15 - 33 pF
68 - 100 pF
15 - 33 pF
XT 100 kHz
2 MHz
4 MHz
100 - 150 pF
15 - 33 pF
15 - 33 pF
100 - 150 pF
15 - 33 pF
15 - 33 pF
HS 4 MHz
20 MHz
15 - 33 pF
15 - 33 pF
15 - 33 pF
15 - 33 pF
Note: 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 V
DD > 4.5V, C1 = C2  30 pF is recom-
mended.
OSC2/CLKOUT
CEXT
REXT
PIC16FXX
OSC1
F
OSC/4
Internal
Clock
VDD
VSS
Recommended values: 5 k  REXT  100 k
C
EXT > 20pF