Datasheet

PIC12(L)F1501
DS41615A-page 46 Preliminary  2011 Microchip Technology Inc.
5.2 Clock Source Types
Clock sources can be classified as external or internal.
External clock sources rely on external circuitry for the
clock source to function. Examples are: oscillator mod-
ules (EC mode).
Internal clock sources are contained within the
oscillator module. The oscillator block has two internal
oscillators that are used to generate two system clock
sources: the 16 MHz High-Frequency Internal
Oscillator (HFINTOSC) and the 31 kHz Low-Frequency
Internal Oscillator (LFINTOSC).
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.
• Clear the SCS<1:0> bits in the OSCCON register
to switch the system clock source to:
- 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 CLKIN input. CLKOUT is
available for general purpose I/O or CLKOUT.
Figure 5-2 shows the pin connections for EC mode.
EC mode has 3 power modes to select from through
Configuration Words:
• High power, 4-20 MHz (FOSC = 11)
• Medium power, 0.5-4 MHz (FOSC = 10)
• Low power, 0-0.5 MHz (FOSC = 01)
When EC mode is selected, there is no delay in opera-
tion after a Power-on Reset (POR) or wake-up from
Sleep. Because the PIC
®
MCU design is fully static,
stopping the external clock input will have the effect of
halting the device while leaving all data intact. Upon
restarting the external clock, the device will resume
operation as if no time had elapsed.
FIGURE 5-2: EXTERNAL CLOCK (EC)
MODE OPERATION
CLKIN
CLKOUT
Clock from
Ext. System
PIC
®
MCU
FOSC/4 or
I/O
(1)
Note 1: Output depends upon CLKOUTEN bit of the
Configuration Words.