PIC16F628-20P Datasheet, PDF (96/170 Pages) Microchip Technology – FLASH-Based 8-Bit CMOS Microcontroller

PIC16F62X
FIGURE 14-2:
EXTERNAL PARALLEL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
+5V
10K
4.7K
74AS04
TO OTHER
DEVICES
74AS04
PIC16F62X
CLKIN
10K
XTAL
10K
C1
C2
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 kΩ resistors provide the negative feedback to bias
the inverters in their linear region.
FIGURE 14-3:
EXTERNAL SERIES
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
330 KΩ
74AS04
330 KΩ
74AS04
0.1 PF
TO OTHER
DEVICES _PIC16F62X
74AS04
CLKIN
XTAL
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)
Clock From
ext. system
RA6
OSC1/RA7
PIC16F62X
OSC2/RA6
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 VSS, 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 REXT values below
10k, the oscillator operation becomes sensitive to
temperature. For very high REXT values (e.g., 1M), the
oscillator becomes sensitive to leakage and may stop
completely. Thus, we recommend keeping REXT
between 10k and 1M.
FIGURE 14-5:
EXTERNAL RESISTOR
RA7/OSC1/CLKIN
RA6/OSC2/CLKOUT
Table 14-3 shows the relationship between the
resistance value and the operating frequency.
TABLE 14-3: RESISTANCE AND
FREQUENCY RELATIONSHIP
Resistance
0
1K
10K
20K
47K
100K
220K
470K
1M
Frequency
10.4 MHz
10 MHz
7.4 MHz
5.3 MHz
3 MHz
1.6 MHz
800 kHz
300 kHz
200 kHz
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 FOSC signal (internal
clock divided by 4) for test or external synchronization
purposes.
DS40300C-page 94
Preliminary
 2003 Microchip Technology Inc.