PIC16F87XA
TABLE 14-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
14.2.3
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 resis-
tor (REXT) and capacitor (CEXT) values, and the operat-
ing temperature. In addition to this, the oscillator
frequency will vary from unit to unit due to normal pro-
cess parameter variation. Furthermore, the difference
in lead frame capacitance between package types will
also affect the oscillation frequency, especially for low
CEXT values. The user also needs to take into account
variation due to tolerance of external R and C compo-
nents used. Figure 14-3 shows how the R/C combina-
tion is connected to the PIC16F87XA.
Crystal
Freq.
Cap. Range Cap. Range
Osc Type
C1
C2
LP
32 kHz
200 kHz
200 kHz
1 MHz
33 pF
15 pF
33 pF
15 pF
XT
HS
47-68 pF
15 pF
47-68 pF
15 pF
4 MHz
15 pF
15 pF
4 MHz
15 pF
15 pF
8 MHz
15-33 pF
15-33 pF
15-33 pF
15-33 pF
20 MHz
FIGURE 14-3:
RC OSCILLATOR MODE
These values are for design guidance only.
See notes following this table.
VDD
Crystals Used
32 kHz
200 kHz
1 MHz
4 MHz
8 MHz
Epson C-001R32.768K-A
STD XTL 200.000KHz
ECS ECS-10-13-1
± 20 PPM
± 20 PPM
± 50 PPM
± 50 PPM
± 30 PPM
REXT
Internal
OSC1
Clock
CEXT
VSS
PIC16F87XA
ECS ECS-40-20-1
EPSON CA-301 8.000M-C
OSC2/CLKOUT
FOSC/4
20 MHz EPSON CA-301 20.000M-C ± 30 PPM
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20pF
Note 1: Higher capacitance increases the stability
of oscillator, but also increases the start-
up time.
2: Since each resonator/crystal has its own
characteristics, the user should consult the
resonator/crystal manufacturer for appro-
priate values of external components.
3: Rs may be required in HS mode, as well
as XT mode, to avoid overdriving crystals
with low drive level specification.
4: When migrating from other PICmicro®
devices, oscillator performance should be
verified.
DS39582A-page 144
AdvanceInformation
2001 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
