
PIC16(L)F722A/723A
DS41417B-page 82
2010-2012 Microchip Technology Inc.
FIGURE 7-4:
CERAMIC RESONATOR
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.
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.
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.
The RC oscillator frequency is a function of the supply
voltage, the resistor (REXT) and capacitor (CEXT) values
and the operating temperature. Other factors affecting
the oscillator frequency are:
threshold voltage variation
component tolerances
packaging variations in capacitance
The user also needs to take into account variation due
to tolerance of external RC components used.
TABLE 7-1:
SUMMARY OF REGISTERS ASSOCIATED WITH CLOCK SOURCES
TABLE 7-2:
SUMMARY OF CONFIGURATION WORD WITH CLOCK SOURCES
Note 1: A series resistor (RS) may be required for
ceramic resonators with low drive level.
2: The value of RF varies with the Oscillator mode
selected.
3: An additional parallel feedback resistor (RP)
may be required for proper ceramic resonator
operation.
C1
C2 Ceramic
RS(1)
OSC1/CLKIN
RF(2)
Sleep
To Internal
Logic
PIC MCU
RP(3)
Resonator
OSC2/CLKOUT
OSC2/CLKOUT(1)
CEXT
REXT
PIC MCU
OSC1/CLKIN
FOSC/4 or
Internal
Clock
VDD
VSS
Recommended values: 10 k
REXT 100 k, <3V
3 k
REXT 100 k, 3-5V
CEXT > 20 pF, 2-5V
Note 1:
Alternate pin functions are described in
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
Register
on Page
OSCCON
—
IRCF1
IRCF0
ICSL
ICSS
—
OSCTUNE
—
TUN5
TUN4
TUN3
TUN2
TUN1
TUN0
Legend: x = unknown, u = unchanged, – = unimplemented locations read as ‘0’. Shaded cells are not used by
oscillators.
Name
Bits
Bit -/7
Bit -/6
Bit 13/5
Bit 12/4
Bit 11/3
Bit 10/2
Bit 9/1
Bit 8/0
Register
on Page
CONFIG1
13:8
—
—DEBUG
PLLEN
—
BORV
BOREN1
BOREN0
7:0
—
CP
MCLRE
PWRTE
WDTE
FOSC<2:0>
Legend:
— = unimplemented location, read as ‘0’. Shaded cells are not used by clock sources.