PIC16F688 Datasheet, PDF (25/174 Pages) Microchip Technology – 14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

3.3.3 LP, XT, HS MODES
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
internal inverter-amplifier to support various resonator
types and speed.
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.
XT Oscillator mode selects the intermediate gain
setting of the internal inverter-amplifier. XT mode cur-
rent consumption is the medium of the three modes.
This mode is best suited to drive resonators with a
medium drive level specification, for example,
low-frequency/AT-cut quartz crystal resonators.
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, for example, high-frequency/AT-cut
quartz crystal resonators or ceramic resonators.
Figure 3-3 and Figure 3-4 show typical circuits for
quartz crystal and ceramic resonators, respectively.
FIGURE 3-3:
QUARTZ CRYSTAL
OPERATION (LP, XT OR
HS MODE)
PIC16F688
OSC1
C1
Quartz
Crystal
OSC2
RS⁽¹⁾
C2
RF⁽²⁾
To Internal
Logic
Sleep
Note 1: A series resistor (RS) may be required for
quartz crystals with low drive level.
2: The value of RF varies with the oscillator
mode selected (typically between 2 MΩ to
10 MΩ).
Note 1: Quartz crystal characteristics vary
according to type, package and manufac-
turer. The user should consult the
manufacturer data sheets for specifica-
tions and recommended application.
2: Always verify oscillator performance over
the VDD and temperature range that is
expected for the application.
PIC16F688
FIGURE 3-4:
CERAMIC RESONATOR
OPERATION
(XT OR HS MODE)
PIC16F688
OSC1
C1
To Internal
Logic
RP⁽³⁾
RF⁽²⁾
Sleep
OSC2
RS⁽¹⁾
C2 _Ceramic
Resonator
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).
3: An additional parallel feedback resistor (RP)
may be required for proper ceramic resonator
operation (typical value 1 MΩ).
 2004 Microchip Technology Inc.
Preliminary
DS41203B-page 23