PIC18F-LF1XK50 Datasheet, PDF (18/420 Pages) Microchip Technology – 20-Pin USB Flash Microcontrollers

PIC18F/LF1XK50
FIGURE 2-3:
CERAMIC RESONATOR
OPERATION
(XT OR HS MODE)
PIC^® MCU
OSC1/CLKIN
C1
To Internal
Logic
RP⁽³⁾
RF⁽²⁾
Sleep
C2 _{Ceramic RS}⁽¹⁾
Resonator
OSC2/CLKOUT
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 M to 10 M.
3: An additional parallel feedback resistor (RP)
may be required for proper ceramic resonator
operation.
2.3.3 EXTERNAL RC
The External Resistor-Capacitor (RC) mode supports
the use of an external RC circuit. This allows the
designer maximum flexibility in frequency choice while
keeping costs to a minimum when clock accuracy is not
required. In RC mode, the RC circuit connects to OSC1,
allowing OSC2 to be configured as an IO or as
CLKOUT. The CLKOUT function is selected by the
FOSC bits of the CONFIG1H Configuration register.
When OSC2 is configured as CLKOUT, the frequency
at the pin is the frequency of the RC oscillator divided by
4. Figure 2-4 shows the external RC mode connections.
FIGURE 2-4:
EXTERNAL RC MODES
VDD
REXT
CEXT
VSS
FOSC/4 or
I/O⁽²⁾
PIC^® MCU
OSC1/CLKIN
Internal
Clock
OSC2/CLKOUT⁽¹⁾
Recommended values: 10 k  REXT  100 k
CEXT > 20 pF
Note 1:
2:
Alternate pin functions are listed in
Section 1.0 “Device Overview”.
Output depends upon RC or RCIO clock mode.
The RC oscillator frequency is a function of the supply
voltage, the resistor REXT, the capacitor CEXT and the
operating temperature. Other factors affecting the
oscillator frequency are:
• Input threshold voltage variation
• Component tolerances
• Variation in capacitance due to packaging
2.3.4 EXTERNAL CLOCK
The External Clock (EC) mode allows an externally
generated logic level clock to be used as the system’s
clock source. When operating in this mode, the
external clock source is connected to the OSC1
allowing OSC2 to be configured as an I/O or as
CLKOUT. The CLKOUT function is selected by the
FOSC bits of the CONFIG1H Configuration register.
When OSC2 is configured as CLKOUT, the frequency
at the pin is the frequency of the EC oscillator divided
by 4.
Three different power settings are available for EC
mode. The power settings allow for a reduced IDD of the
device, if the EC clock is known to be in a specific
range. If there is an expected range of frequencies for
the EC clock, select the power mode for the highest
frequency.
EC Low power
0 – 250 kHz
EC Medium power 250 kHz – 4 MHz
EC High power 4 – 48 MHz
2.4 Secondary External Oscillator
The Secondary External Oscillator is designed to drive
an external 32.768 kHz crystal. This oscillator is
enabled or disabled by the T1OSCEN bit of the T1CON
register. See Section 11.0 “Timer1 Module” for more
information.
DS41350E-page 18
Preliminary
 2010 Microchip Technology Inc.