PIC16F7X Datasheet, PDF (94/174 Pages) Microchip Technology – 28/40-Pin 8-Bit CMOS FLASH Microcontrollers

PIC16F7X
TABLE 12-2:
CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
(FOR DESIGN GUIDANCE
ONLY)
Osc Type
Crystal
Freq
Typical Capacitor Values
Tested:
C1
C2
LP
32 kHz
33 pF
33 pF
200 kHz
15 pF
15 pF
XT
200 kHz
56 pF
56 pF
1 MHz
15 pF
15 pF
4 MHz
15 pF
15 pF
HS
4 MHz
15 pF
15 pF
8 MHz
15 pF
15 pF
20 MHz
15 pF
15 pF
Capacitor values are for design guidance only.
These capacitors were tested with the crystals listed
below for basic start-up and operation. These values
were not optimized.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
VDD and temperature range for the application.
See the notes following this table for additional
information.
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
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: Always verify oscillator performance over
the VDD and temperature range that is
expected for the application.
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 PIC16F7X.
FIGURE 12-3:
RC OSCILLATOR MODE
VDD
REXT
OSC1
Internal
Clock
CEXT
PIC16F7X
VSS
OSC2/CLKOUT
FOSC/4
Recommended values:
3 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20pF
DS30325B-page 92
 2002 Microchip Technology Inc.