PIC16F631/677/685/687/689/690
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 consumption
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.
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.
Analysis and Design” (DS00943)
• AN949, “Making Your Oscillator Work”
(DS00949)
Figure 3-3 and Figure 3-4 show typical circuits for
quartz crystal and ceramic resonators, respectively.
FIGURE 3-4:
CERAMIC RESONATOR
OPERATION
(XT OR HS MODE)
FIGURE 3-3:
QUARTZ CRYSTAL
OPERATION (LP, XT OR
HS MODE)
PIC® MCU
OSC1/CLKIN
PIC® MCU
C1
To Internal
Logic
OSC1/CLKIN
(3)
(2)
RP
RF
C1
Sleep
To Internal
Logic
Quartz
Crystal
(2)
RF
Sleep
OSC2/CLKOUT
(1)
C2
RS
Ceramic
Resonator
OSC2/CLKOUT
(1)
C2
RS
Note 1: A series resistor (RS) may be required for
ceramic resonators with low drive level.
Note 1: A series resistor (RS) may be required for
2: The value of RF varies with the Oscillator mode
selected (typically between 2 MΩ to 10 MΩ).
quartz crystals with low drive level.
2: The value of RF varies with the Oscillator mode
selected (typically between 2 MΩ to 10 MΩ).
3: An additional parallel feedback resistor (RP)
may be required for proper ceramic resonator
operation.
DS41262D-page 50
© 2007 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
