PIC16HV785-I/SO View Datasheet(PDF) - Microchip Technology
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PIC16HV785-I/SO Datasheet PDF : 206 Pages
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PIC16F785/HV785
TABLE 3-3: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Osc Type
Crystal
Freq.
Cap. Range Cap. Range
C1
C2
LP
32 kHz 15-33 pF
15-33 pF
XT
200 kHz 47-68 pF
47-68 pF
1 MHz 15-33 pF
15-33 pF
4 MHz 15-33 pF
15-33 pF
HS
4 MHz 15-33 pF
15-33 pF
8 MHz 15-33 pF
15-33 pF
20 MHz 15-33 pF
15-33 pF
Note: These values are for design guidance
only. See notes following this table.
Note 1: Higher capacitance increases the stability
of the 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: RS may be required to avoid overdriving
crystals with low drive level specification.
3.3.4 EXTERNAL RC MODES
The External Resistor-Capacitor (RC) modes support
the use of an external RC circuit. This allows the
designer maximum flexibility in frequency choice while
keeping costs to a minimum when clock accuracy is not
required. There are two modes, RC and RCIO.
In RC mode, the RC circuit connects to the OSC1 pin.
The OSC2/CLKOUT pin outputs the RC oscillator
frequency divided by 4. This signal may be used to
provide a clock for external circuitry, synchronization,
calibration, test or other application requirements.
Figure 3-5 shows the RC mode connections.
FIGURE 3-5:
VDD
RC MODE
REXT
OSC1
Internal
Clock
CEXT
PIC16F785/HV785
VSS
OSC2/CLKOUT
FOSC/4
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ (VDD ≥ 3.0V)
10 kΩ ≤ REXT ≤ 100 kΩ (VDD < 3.0V)
CEXT > 20 pF
In RCIO mode, the RC circuit is connected to the OSC1
pin. The OSC2 pin becomes an additional general
purpose I/O pin. The I/O pin becomes bit 4 of PORTA
(RA4). Figure 3-6 shows the RCIO mode connections.
FIGURE 3-6:
VDD
RCIO MODE
REXT
CEXT
VSS
RA4
OSC1
Internal
Clock
PIC16F785/HV785
I/O (OSC2)
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ (VDD ≥ 3.0V)
10 kΩ ≤ REXT ≤ 100 kΩ (VDD < 3.0V)
CEXT > 20 pF
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 threshold voltage. Furthermore, the dif-
ference in lead frame capacitance between package
types will also affect the oscillation frequency or low
CEXT values. The user also needs to take into account
variation due to tolerance of external RC components
used.
DS41249E-page 26
© 2008 Microchip Technology Inc.
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