Datasheet

PIC12(L)F1501
DS40001615C-page 44  2011-2015 Microchip Technology Inc.
5.2 Clock Source Types
Clock sources can be classified as external, internal or
peripheral.
External clock sources rely on external circuitry for the
clock source to function. Examples are: oscillator mod-
ules (ECH, ECM, ECL modes).
Internal clock sources are contained within the oscillator
module. The internal oscillator block has two internal
oscillators that are used to generate the internal system
clock sources: the 16 MHz High-Frequency Internal
Oscillator (HFINTOSC) and the 31 kHz Low-Frequency
Internal Oscillator (LFINTOSC).
The peripheral clock source is a nominal 600 kHz
internal RC oscillator, FRC. The FRC is traditionally
used with the ADC module, but is sometimes available
to other peripherals. See Section 5.2.2.4 “Peripheral
Clock Sources”.
The system clock can be selected between external or
internal clock sources via the System Clock Select
(SCS) bits in the OSCCON register. See Section
5.3 “Clock Switching” for additional information.
5.2.1 EXTERNAL CLOCK SOURCES
An external clock source can be used as the device
system clock by performing one of the following
actions:
• Program the FOSC<1:0> bits in the Configuration
Words to select an external clock source that will
be used as the default system clock upon a
device Reset.
• Write the SCS<1:0> bits in the OSCCON register
to switch the system clock source to:
- Secondary oscillator during run-time, or
- An external clock source determined by the
value of the FOSC bits.
See Section 5.3 “Clock Switching” for more informa-
tion.
5.2.1.1 EC Mode
The External Clock (EC) mode allows an externally
generated logic level signal to be the system clock
source. When operating in this mode, an external clock
source is connected to the OSC1 input.
OSC2/CLKOUT is available for general purpose I/O or
CLKOUT. Figure 5-2 shows the pin connections for EC
mode.
EC mode has three power modes to select from through
the F
OSC bits in the Configuration Words:
• ECH – High power, 4-20 MHz
• ECM – Medium power, 0.5-4 MHz
• ECL – Low power, 0-0.5 MHz
FIGURE 5-2: EXTERNAL CLOCK (EC)
MODE OPERATION
Clock from
Ext. system
F OSC /4 or I/O
(1)
OSC1/CLKIN
PIC
®
MCU
OSC2/CLKOUT
Note 1: Output depends upon the CLKOUTEN bit
of the Configuration Words.
Rev. 10-000045A
7/30/2013