PIC12F508-E Datasheet, PDF (44/106 Pages) Microchip Technology – 8/14-Pin, 8-Bit Flash Microcontrollers

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).
When the part is used in this fashion, the output drive
levels on the OSC2 pin are very weak. This pin should
be left open and unloaded. Also, when using this mode,
the external clock should observe the frequency limits
for the clock mode chosen (HS, XT or LP).
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.
FIGURE 7-1:
CRYSTAL OPERATION
(OR CERAMIC
RESONATOR)
(HS, XT OR LP OSC
CONFIGURATION)
C1⁽¹⁾
OSC1
PIC12F508/509
PIC16F505
XTAL
OSC2
RS⁽²⁾
C2⁽¹⁾
RF⁽³⁾
Sleep
To internal
logic
Note 1:
2:
3:
See Capacitor Selection tables for
recommended values of C1 and C2.
A series resistor (RS) may be required for AT
strip cut crystals.
RF approx. value = 10 MΩ.
FIGURE 7-2:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSC
CONFIGURATION)
Clock from
ext. system
Open
OSC1
PIC12F508/509
PIC16F505
OSC2
TABLE 7-1:
CAPACITOR SELECTION FOR
CERAMIC RESONATORS –
PIC12F508/509/16F505⁽¹⁾
Osc Resonator Cap. Range Cap. Range
Type
Freq.
C1
C2
XT
HS⁽²⁾
Note 1:
2:
4.0 MHz
30 pF
30 pF
16 MHz
10-47 pF
10-47 pF
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.
PIC16F505 only.
DS41236D-page 42
Preliminary
© 2007 Microchip Technology Inc.