PIC16LF1904 Datasheet, PDF (59/288 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt XLP Technology

6.2 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. An example is: oscillator mod-
ule (EC mode) circuit.
Internal clock sources are contained internally 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 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 6.3
“Clock Switching” for additional information.
6.2.1 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
Word 1 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 6.3 “Clock Switching”for more informa-
tion.
6.2.1.1 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 6-2 shows the pin connections for EC mode.
EC mode has 3 power modes to select from through
Configuration Word 1:
• High power, 4-20 MHz (FOSC = 11)
• Medium power, 0.5-4 MHz (FOSC = 10)
• Low power, 0-0.5 MHz (FOSC = 01)
PIC16LF1904/6/7
The Oscillator Start-up Timer (OST) is disabled when
EC mode is selected. Therefore, there is no delay in
operation 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 6-2:
EXTERNAL CLOCK (EC)
MODE OPERATION
Clock from
Ext. System
FOSC/4 or I/O⁽¹⁾
CLKIN
PIC^® MCU
CLKOUT
Note 1: Output depends upon CLKOUTEN bit of the
Configuration Word 1.
 2011 Microchip Technology Inc.
Preliminary
DS41569A-page 59