Microchip Technology AC244045 Data Sheet
PIC16F72X/PIC16LF72X
DS41341E-page 94
© 2009 Microchip Technology Inc.
FIGURE 7-4:
CERAMIC RESONATOR
OPERATION
(XT OR HS MODE)
OPERATION
(XT OR HS MODE)
7.6.4
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.
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 OSC1.
OSC2/CLKOUT 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 7-5 shows
the external RC mode connections.
OSC2/CLKOUT 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 7-5 shows
the external RC mode connections.
FIGURE 7-5:
EXTERNAL RC MODES
In RCIO mode, the RC circuit is connected to OSC1.
OSC2 becomes an additional general purpose I/O pin.
OSC2 becomes an additional general purpose I/O pin.
The RC oscillator frequency is a function of the supply
voltage, the resistor (R
voltage, the resistor (R
EXT
) and capacitor (C
EXT
) values
and the operating temperature. Other factors affecting
the oscillator frequency are:
the oscillator frequency are:
• threshold voltage variation
• component tolerances
• packaging variations in capacitance
• component tolerances
• packaging variations in capacitance
The user also needs to take into account variation due
to tolerance of external RC components used.
to tolerance of external RC components used.
TABLE 7-1:
SUMMARY OF REGISTERS ASSOCIATED WITH CLOCK SOURCES
Note
1: A series resistor (R
S
) may be required for
ceramic resonators with low drive level.
2: The value of R
F
varies with the Oscillator mode
selected.
3: An additional parallel feedback resistor (R
P
)
may be required for proper ceramic resonator
operation.
operation.
C1
C2 Ceramic
R
S
(1)
OSC1/CLKIN
R
F
(2)
Sleep
To Internal
Logic
Logic
PIC
®
MCU
R
P
(3)
Resonator
OSC2/CLKOUT
OSC2/CLKOUT
(1)
C
EXT
R
EXT
PIC
®
MCU
OSC1/CLKIN
F
OSC
/4 or
Internal
Clock
V
DD
V
SS
Recommended values: 10 k
Ω ≤ R
EXT
≤ 100 kΩ, <3V
3 k
Ω ≤ R
EXT
≤ 100 kΩ, 3-5V
C
EXT
> 20 pF, 2-5V
Note
1:
Alternate pin functions are described in
Section 6.1 “Alternate Pin Function”.
Section 6.1 “Alternate Pin Function”.
2:
Output depends upon RC or RCIO clock mode.
I/O
(2)
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
POR, BOR
Value on
all other
Resets
(1)
CONFIG1
(1)
—
CP
MCLRE
PWRTE
WDTE
FOSC2
FOSC1
FOSC0
—
—
OSCCON
—
—
IRCF1
IRCF0
ICSL
ICSS
—
—
--10 qq--
--10 qq--
OSCTUNE
—
—
TUN5
TUN4
TUN3
TUN2
TUN1
TUN0
--00 0000
--uu uuuu
Legend:
x
= unknown, u = unchanged, – = unimplemented locations read as ‘0’. Shaded cells are not used by oscillators.
Note
1:
See Configuration Word 1 (Register 8-1) for operation of all bits.