Datasheet

© 2008 Microchip Technology Inc. DS41249E-page 25
PIC16F785/HV785
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 inter-
nal 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 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.
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.
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)
FIGURE 3-4: CERAMIC RESONATOR
OPERATION
(XT OR HS MODE)
TABLE 3-2: CERAMIC RESONATORS
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.
2: Always verify oscillator performance over
the V
DD and temperature range that is
expected for the application.
Note 1: A series resistor (RS) may be required for
quartz crystals with low drive level.
2: The value of R
F varies with the Oscillator
mode selected (typically between 2 MΩ to
10 MΩ).
C1
C2
Quartz
OSC2
R
S
(1)
OSC1
RF
(2)
Sleep
To Internal
Logic
Crystal
PIC16F785/HV785
Mode Freq. OSC1 (C1) OSC2 (C2)
XT 455 kHz
2.0 MHz
68-100 pF
15-68 pF
68-100 pF
15-68 pF
HS 4.0 MHz
8.0 MHz
16.0 MHz
10-68 pF
15-68 pF
10-22 pF
10-68 pF
15-68 pF
10-22 pF
Note: These values are for design guidance
only. See notes following this table.
Note 1: A series resistor (RS) may be required for
ceramic resonators with low drive level.
2: The value of R
F varies with the Oscillator
mode selected (typically between 2 MΩ to
10 MΩ).
3: An additional parallel feedback resistor (R
P)
may be required for proper ceramic resonator
operation (typical value 1 MΩ).
C1
C2
Ceramic
OSC2
R
S
(1)
OSC1
RF
(2)
Sleep
To Internal
Logic
RP
(3)
Resonator
PIC16F785/HV785