PIC12F683
3.3.3
LP, XT, HS MODES
FIGURE 3-4:
CERAMIC RESONATOR
OPERATION
(XT OR HS MODE)
The LP, XT and HS modes support the use of quartz
crystal resonators or ceramic resonators connected to
the OSC1 and OSC2 pins (Figure 3-1). The mode
selects a low, medium or high gain setting of the inter-
nal inverter-amplifier to support various resonator
types and speed.
PIC12F683
OSC1
C1
C2
To Internal
Logic
LP Oscillator mode selects the lowest gain setting of
the internal inverter-amplifier. LP mode current con-
sumption is the least of the three modes. This mode is
best suited to drive resonators with a low drive level
specification, for example, tuning fork type crystals.
(3)
(2)
RF
Sleep
RP
OSC2
(1)
RS
Ceramic
Resonator
XT Oscillator mode selects the intermediate gain set-
ting of the internal inverter-amplifier. XT mode current
consumption is the medium of the three modes. This
mode is best suited to drive resonators with a medium
drive level specification, for example, AT-cut quartz
crystal resonators.
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 (typically between 2 MΩ to
10 MΩ).
HS Oscillator mode selects the highest gain setting of
the internal inverter-amplifier. HS mode current con-
sumption is the highest of the three modes. This mode
is best suited for resonators that require a high drive
setting, for example, AT-cut quartz crystal resonators or
ceramic resonators.
3: An additional parallel feedback resistor (RP)
may be required for proper ceramic resonator
operation (typical value 1 MΩ).
3.3.4
EXTERNAL RC MODES
Figure 3-3 and Figure 3-4 show typical circuits for
quartz crystal and ceramic resonators, respectively.
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.
FIGURE 3-3:
QUARTZ CRYSTAL
OPERATION (LP, XT OR
HS MODE)
In RC mode, the RC circuit connects to the OSC1 pin.
The OSC2/CLKOUT pin outputs the RC oscillator fre-
quency divided by 4. This signal may be used to provide
a clock for external circuitry, synchronization, calibra-
tion, test or other application requirements. Figure 3-5
shows the RC mode connections.
PIC12F683
OSC1
C1
To Internal
Logic
FIGURE 3-5:
RC MODE
Quartz
Crystal
(2)
RF
Sleep
VDD
OSC2
(1)
RS
REXT
C2
Internal
Clock
OSC1
Note 1: A series resistor (RS) may be required for
CEXT
VSS
quartz crystals with low drive level.
PIC12F683
OSC2/CLKOUT
2: The value of RF varies with the oscillator
mode selected (typically between 2 MΩ to
10 MΩ).
FOSC/4
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20 pF
Note 1: Quartz crystal characteristics vary
according to type, package and manufac-
turer. The user should consult the manu-
facturer data sheets for specifications and
recommended application.
In RCIO mode, the RC circuit is connected to the OSC1
pin. The OSC2 pin becomes an additional general pur-
pose I/O pin. The I/O pin becomes bit 4 of GPIO (GP4).
Figure 3-6 shows the RCIO mode connections.
2: Always verify oscillator performance over
the VDD and temperature range that is
expected for the application.
2004 Microchip Technology Inc.
Preliminary
DS41211B-page 21
MICROCHIP [ MICROCHIP ]
