PIC16F688
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
best suited to drive resonators with a low drive level
specification, for example, tuning fork type crystals.
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)
• AN949, “Making Your Oscillator Work”
(DS00949)
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.
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)
PIC® MCU
FIGURE 3-3:
QUARTZ CRYSTAL
OPERATION (LP, XT OR
HS MODE)
OSC1/CLKIN
C1
To Internal
Logic
PIC® MCU
(3)
(2)
RP
RF
Sleep
OSC1/CLKIN
C1
To Internal
Logic
OSC2/CLKOUT
(1)
C2
RS
Ceramic
Resonator
Quartz
Crystal
(2)
Sleep
RF
Note 1: A series resistor (RS) may be required for
ceramic resonators with low drive level.
OSC2/CLKOUT
(1)
C2
RS
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
3: An additional parallel feedback resistor (RP)
may be required for proper ceramic resonator
operation.
quartz crystals with low drive level.
2: The value of RF varies with the Oscillator mode
selected (typically between 2 MΩ to 10 MΩ).
DS41203D-page 24
© 2007 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
