Datasheet

© 2005 Microchip Technology Inc. Preliminary DS41236B-page 41
PIC12F508/509/16F505
7.2 Oscillator Configurations
7.2.1 OSCILLATOR TYPES
The PIC12F508/509/16F505 devices can be operated
in up to six different oscillator modes. The user can
program up to three configuration bits (FOSC<1:0>
[PIC12F508/509], FOSC<2:0> [PIC16F505]). To select
one of these modes:
• LP: Low-Power Crystal
• XT: Crystal/Resonator
• HS: High-Speed Crystal/Resonator
(PIC16F505 only)
• INTRC: Internal 4 MHz Oscillator
• EXTRC: External Resistor/Capacitor
• EC: External High-Speed Clock Input
(PIC16F505 only)
7.2.2 CRYSTAL OSCILLATOR/CERAMIC
RESONATORS
In HS (PIC16F505), XT or LP modes, a crystal or
ceramic resonator is connected to the (GP5/RB5)/
OSC1/(CLKIN) and (GP4/RB4)/OSC2/(CLKOUT) pins
to establish oscillation (Figure 7-1). The PIC12F508/
509/16F505 oscillator designs require the use of a
parallel cut crystal. Use of a series cut crystal may give
a frequency out of the crystal manufacturers
specifications. When in HS (PIC16F505), XT or LP
modes, the device can have an external clock source
drive the (GP5/RB5)/OSC1/CLKIN pin (Figure 7-2).
FIGURE 7-1: CRYSTAL OPERATION
(OR CERAMIC
RESONATOR)
(HS, XT OR LP OSC
CONFIGURATION)
FIGURE 7-2: EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSC
CONFIGURATION)
TABLE 7-1: CAPACITOR SELECTION FOR
CERAMIC RESONATORS –
PIC12F508/509/16F505
(1)
Note 1: This device has been designed to per-
form to the parameters of its data sheet.
It has been tested to an electrical
specification designed to determine its
conformance with these parameters.
Due to process differences in the
manufacture of this device, this device
may have different performance charac-
teristics than its earlier version. These
differences may cause this device to
perform differently in your application
than the earlier version of this device.
2: The user should verify that the device
oscillator starts and performs as
expected. Adjusting the loading capacitor
values and/or the Oscillator mode may
be required.
Osc
Type
Resonator
Freq.
Cap. Range
C1
Cap. Range
C2
XT 4.0 MHz 30 pF 30 pF
HS
(2)
16 MHz 10-47 pF 10-47 pF
Note 1: These values are for design guidance
only. Since each resonator has its own
characteristics, the user should consult
the resonator manufacturer for
appropriate values of external
components.
2: PIC16F505 only.
Note 1: See Capacitor Selection tables for
recommended values of C1 and C2.
2: A series resistor (RS) may be required for AT
strip cut crystals.
3: RF approx. value = 10 MΩ.
C1
(1)
C2
(1)
XTAL
OSC2
OSC1
RF
(3)
Sleep
To internal
logic
RS
(2)
PIC12F508/509
PIC16F505
Clock from
ext. system
OSC1
OSC2
PIC16F505
Open
PIC12F508/509