PIC16F872 Datasheet, PDF (98/160 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH Microcontroller

PIC16F872
TABLE 11-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Osc
Type
Crystal
Freq
Cap. Range
C1
Cap.
Range
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 at bottom of page.
Crystals Used
32 kHz Epson C-001R32.768K-A ± 20 PPM
200 kHz STD XTL 200.000KHz
± 20 PPM
1 MHz ECS ECS-10-13-1
± 50 PPM
4 MHz ECS ECS-40-20-1
± 50 PPM
8 MHz EPSON CA-301 8.000M-C ± 30 PPM
20 MHz EPSON CA-301 20.000M-C ± 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 compo-
nents.
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.
11.2.3 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 11-3 shows how the R/C combina-
tion is connected to the PIC16F872.
FIGURE 11-3: RC OSCILLATOR MODE
VDD
REXT
OSC1
Internal
Clock
CEXT
PIC16F872
VSS
OSC2/CLKOUT
FOSC/4
Recommended values:
3 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20pF
DS30221A-page 98
Preliminary
© 1999 Microchip Technology Inc.