PIC16F87X Datasheet, PDF (124/218 Pages) Microchip Technology – 28/40-pin 8-Bit CMOS FLASH Microcontrollers

PIC16F87X
TABLE 12-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Osc Type
Crystal
Freq.
Cap. Range Cap. Range
C1
C2
LP
32 kHz
200 kHz
33 pF
15 pF
33 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
200 kHz
1 MHz
4 MHz
8 MHz
20 MHz
Epson C-001R32.768K-A
STD XTL 200.000KHz
ECS ECS-10-13-1
ECS ECS-40-20-1
EPSON CA-301 8.000M-C
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 appro-
priate 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.
12.2.3 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 12-3 shows how the R/C combina-
tion is connected to the PIC16F87X.
FIGURE 12-3:
RC OSCILLATOR MODE
VDD
REXT
OSC1
Internal
Clock
CEXT
PIC16F87X
VSS
OSC2/CLKOUT
FOSC/4
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20pF
DS30292C-page 122
 2001 Microchip Technology Inc.