PIC16F87XA Datasheet, PDF (148/234 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers

PIC16F87XA
TABLE 14-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Osc Type
Crystal
Freq.
Cap. Range Cap. Range
C1
C2
LP
32 kHz
33 pF
33 pF
200 kHz
15 pF
15 pF
XT
200 kHz
47-68 pF
47-68 pF
1 MHz
15 pF
15 pF
4 MHz
15 pF
15 pF
HS
4 MHz
15 pF
15 pF
8 MHz
15-33 pF
15-33 pF
20 MHz
15-33 pF
15-33 pF
These values are for design guidance only.
See notes following this table.
Crystals Used
32 kHz Epson C-001R32.768K-A
200 kHz STD XTL 200.000KHz
1 MHz
ECS ECS-10-13-1
4 MHz
ECS ECS-40-20-1
8 MHz EPSON CA-301 8.000M-C
20 MHz EPSON CA-301 20.000M-C
± 20 PPM
± 20 PPM
± 50 PPM
± 50 PPM
± 30 PPM
± 30 PPM
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
appropriate values of external
components.
3: R_s 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.
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
resistor (REXT) and capacitor (CEXT) values and the
operating 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
components used. Figure 14-3 shows how the R/C
combination is connected to the PIC16F87XA.
FIGURE 14-3:
VDD
RC OSCILLATOR MODE
REXT
OSC1
Internal
Clock
CEXT
VSS
PIC16F87XA
OSC2/CLKO
FOSC/4
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20 pF
DS39582B-page 146
 2003 Microchip Technology Inc.