PIC16F62X
DS40300C-page 94
Preliminary
2003 Microchip Technology Inc.
FIGURE 14-2:
EXTERNAL PARALLEL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
Figure 14-3 shows a series resonant oscillator circuit.
This circuit is also designed to use the fundamental
frequency of the crystal. The inverter performs a 180
°
phase shift in a series resonant oscillator circuit. The
330 k
resistors provide the negative feedback to bias
the inverters in their linear region.
FIGURE 14-3:
EXTERNAL SERIES
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
14.2.4
EXTERNAL CLOCK IN
For applications, where a clock is already available
elsewhere, users may directly drive the PIC16F62X
provided that this external clock source meets the
AC/DC timing requirements listed in Section 17.4.
Figure 14-4 shows how an external clock circuit should
be configured.
FIGURE 14-4:
EXTERNAL CLOCK INPUT
OPERATION (EC, HS, XT
OR LP OSC
CONFIGURATION)
14.2.5
ER OSCILLATOR
For timing insensitive applications, the ER (External
Resistor) Clock mode offers additional cost savings.
Only one external component, a resistor to V
SS
, is
needed to set the operating frequency of the internal
oscillator. The resistor draws a DC bias current which
controls the oscillation frequency. In addition to the
resistance value, the oscillator frequency will vary from
unit to unit, and as a function of supply voltage and
temperature. Since the controlling parameter is a DC
current and not a capacitance, the particular package
type and lead frame will not have a significant effect on
the resultant frequency.
Figure 14-5 shows how the controlling resistor is
connected to the PIC16F62X. For R
EXT
values below
10k, the oscillator operation becomes sensitive to
temperature. For very high R
EXT
values (e.g., 1M), the
oscillator becomes sensitive to leakage and may stop
completely. Thus, we recommend keeping R
EXT
between 10k and 1M.
FIGURE 14-5:
EXTERNAL RESISTOR
Table 14-3 shows the relationship between the
resistance value and the operating frequency.
TABLE 14-3:
RESISTANCE AND
FREQUENCY RELATIONSHIP
The ER Oscillator mode has two options that control
the unused OSC2 pin. The first allows it to be used as
a general purpose I/O port. The other configures the
pin as an output providing the F
OSC
signal (internal
clock divided by 4) for test or external synchronization
purposes.
+5V
10K
4.7K
10K
74AS04
XTAL
10K
74AS04
PIC16F62X
CLKIN
TO OTHER
DEVICES
C1
C2
330 K
74AS04
74AS04
PIC16F62X
CLKIN
TO OTHER
DEVICES
XTAL
330 K
74AS04
0.1 PF
Clock From
ext. system
PIC16F62X
OSC1/RA7
OSC2/RA6
RA6
Resistance
Frequency
0
10.4 MHz
1K
10 MHz
10K
7.4 MHz
20K
5.3 MHz
47K
3 MHz
100K
1.6 MHz
220K
800 kHz
470K
300 kHz
1M
200 kHz
RA7/OSC1/CLKIN
RA6/OSC2/CLKOUT