PIC12F635/PIC16F636/639
3.4.3
LP, XT, HS MODES
Note 1: Quartz crystal characteristics vary according
to type, package and manufacturer. The
user should consult the manufacturer data
sheets for specifications and recommended
application.
The LP, XT and HS modes support the use of quartz
crystal resonators or ceramic resonators connected to
OSC1 and OSC2 (Figure 3-3). The mode selects a low,
medium or high gain setting of the internal
inverter-amplifier to support various resonator types
and speed.
2: Always verify oscillator performance over
the VDD and temperature range that is
expected for the application.
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
designed to drive only 32.768 kHz tuning-fork type
crystals (watch crystals).
3: For oscillator design assistance, reference
the following Microchip Applications Notes:
• AN826, “Crystal Oscillator Basics and
Crystal Selection for rfPIC® and PIC®
Devices” (DS00826)
• AN849, “Basic PIC® Oscillator Design”
(DS00849)
• AN943, “Practical PIC® Oscillator
XT Oscillator mode selects the intermediate gain
setting 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.
Analysis and Design” (DS00943)
HS Oscillator mode selects the highest gain setting of the
internal inverter-amplifier. HS mode current consumption
is the highest of the three modes. This mode is best
suited for resonators that require a high drive setting.
• AN949, “Making Your Oscillator Work”
(DS00949)
FIGURE 3-4:
CERAMIC RESONATOR
OPERATION
Figure 3-3 and Figure 3-4 show typical circuits for
quartz crystal and ceramic resonators, respectively.
(XT OR HS MODE)
FIGURE 3-3:
QUARTZ CRYSTAL
OPERATION (LP, XT OR
HS MODE)
PIC® MCU
OSC1/CLKIN
C1
PIC® MCU
To Internal
Logic
OSC1/CLKIN
(3)
(2)
RP
RF
Sleep
C1
To Internal
Logic
Quartz
Crystal
(2)
OSC2/CLKOUT
(1)
C2
RF
Sleep
RS
Ceramic
Resonator
Note 1: A series resistor (RS) may be required for
OSC2/CLKOUT
(1)
C2
RS
ceramic resonators with low drive level.
2: The value of RF varies with the Oscillator mode
selected (typically between 2 MΩ to 10 MΩ).
Note 1: A series resistor (RS) may be required for
quartz crystals with low drive level.
3: An additional parallel feedback resistor (RP)
may be required for proper ceramic resonator
operation.
2: The value of RF varies with the Oscillator mode
selected (typically between 2 MΩ to 10 MΩ).
DS41232D-page 38
© 2007 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
