PIC16F753 Datasheet, PDF (38/238 Pages) Microchip Technology – 14/16-Pin, Flash-Based 8-Bit CMOS Microcontrollers

PIC16F753/HV753
4.2 Clock Source Modes
Clock Source modes can be classified as external or
internal:
• The External Clock mode relies on an external
clock for the clock source. For example, a clock
module or clock output from another circuit.
• Internal clock sources are contained internally
within the oscillator module. The oscillator module
has four selectable clock frequencies:
- 8 MHz
- 4 MHz
- 1 MHz
- 31 kHz
The system clock can be selected between external or
internal clock sources via the FOSC0 bit of the
Configuration Word register (CONFIG).
4.2.1 EC MODE
The External Clock (EC) mode allows an externally
generated logic as the system clock source. The EC
clock mode is selected when the FOSC0 bit of the
Configuration Word is set.
When operating in this mode, an external clock source
must be connected to the CLKIN input. The CLKOUT is
available for either general purpose I/O or system clock
output. Figure 4-3 shows the pin connections for EC
mode.
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 4-3:
EXTERNAL CLOCK (EC)
MODE OPERATION
Clock from
Ext. System
I/O
CLKIN
PIC^® MCU
CLKOUT⁽¹⁾
Note 1: Alternate pin functions are listed in
Section 1.0 “Device Overview”.
4.2.2 INTERNAL CLOCK MODE
Internal Clock mode configures the internal oscillators
as the system clock source. The Internal Clock mode is
selected when the FOSC0 bit of the Configuration
Word is cleared. The source and frequency are
selected with the IRCF<1:0> bits of the OSCCON
register.
When one of the HFINTOSC frequencies is selected,
the frequency of the internal oscillator can be trimmed
by adjusting the TUN<4:0> bits of the OSCTUNE
register.
Operation after a Power-on Reset (POR) or wake-up
from Sleep is delayed by the oscillator start-up time.
Delays are typically longer for the LFINTOSC than
HFINTOSC because of the very low-power operation
and relatively narrow bandwidth of the LF internal
oscillator. However, when another peripheral keeps the
oscillator running during Sleep, the start-up time is
delayed to allow the memory bias to stabilize.
FIGURE 4-4:
INTERNAL CLOCK MODE
OPERATION
I/O
CLKIN⁽¹⁾
PIC^® MCU
I/O
CLKOUT⁽¹⁾
Note 1: Alternate pin functions are listed in
Section 1.0 “Device Overview”.
4.2.2.1 Oscillator Ready Bits
The HTS and LTS bits of the OSCCON register indicate
the status of the HFINTOSC and LFINTOSC,
respectively. When either bit is set, it indicates that the
corresponding oscillator is running and stable.
DS40001709A-page 38
Preliminary
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