PIC16F193X Datasheet, PDF (111/418 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

PIC16F193X/LF193X
8.3 Clock Source Modes
Clock Source modes can be classified as external or
internal.
• External Clock modes rely on external circuitry for
the clock source. Examples are: oscillator mod-
ules (EC mode), quartz crystal resonators or
ceramic resonators (LP, XT and HS modes) and
Resistor-Capacitor (RC) mode circuits.
• Internal clock sources are contained internally
within the oscillator module. The oscillator module
has two internal oscillators: the 16 MHz
High-Frequency Internal Oscillator (HFINTOSC),
500 kHZ (MFINTOSC) 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) bit of the OSCCON register. See Section 8.6
“Clock Switching” for additional information. When
switching between clock sources, a delay is required to
allow the new clock to stabilize. These oscillator delays
are shown in Table 8-1.
8.4 External Clock Modes
8.4.1 OSCILLATOR START-UP TIMER (OST)
If the oscillator module is configured for LP, XT or HS
modes, the Oscillator Start-up Timer (OST) counts
1024 oscillations from OSC1. This occurs following a
Power-on Reset (POR) and when the Power-up Timer
(PWRT) has expired (if configured), or a wake-up from
Sleep. During this time, the program counter does not
increment and program execution is suspended. The
OST ensures that the oscillator circuit, using a quartz
crystal resonator or ceramic resonator, has started and
is providing a stable system clock to the oscillator
module.
In order to minimize latency between external oscillator
start-up and code execution, the Two-Speed Clock
Start-up mode can be selected (see Section 8.6.3
“Timer1 Oscillator Ready (T1OSCR) Bit”).
TABLE 8-1: OSCILLATOR SWITCHING DELAYS
Switch From
Sleep/POR
Sleep/POR
LFINTOSC
Sleep/POR
Any clock source
Any clock source
Any clock source
PLL inactive
Note 1: PLL inactive.
Switch To
LFINTOSC⁽¹⁾
MFINTOSC⁽¹⁾
HFINTOSC⁽¹⁾
EC, RC⁽¹⁾
EC, RC⁽¹⁾
Timer1 Oscillator
LP, XT, HS⁽¹⁾
MFINTOSC⁽¹⁾
HFINTOSC⁽¹⁾
LFINTOSC⁽¹⁾
Timer1 Oscillator
PLL active
Frequency
31 kHz
31.25 kHz-500 kHz
31.25 kHz-16 MHz
DC – 32 MHz
DC – 32 MHz
32 kHz-20 MHz
31.25 kHz-500 kHz
31.25 kHz-16 MHz
31 kHz
32 kHz
16-32 MHz
Oscillator Delay
Oscillator Warm-up Delay (TWARM)
2 cycles
1 cycle of each
1024 Clock Cycles (OST)
2 μs (approx.)
1 cycle of each
1024 Clock Cycles (OST)
2 ms (approx.)
8.4.2 EC MODE
The External Clock (EC) mode allows an externally
generated logic level as 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 8-2 shows the pin connections for EC mode.
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 8-2:
EXTERNAL CLOCK (EC)
MODE OPERATION
Clock from
Ext. System
FOSC/4 or
I/O⁽¹⁾
OSC1/CLKIN
PIC^® MCU
OSC2/CLKOUT⁽¹⁾
Note 1: Output depends upon CLKOUTEN bit of the
Configuration Word 1.
© 2008 Microchip Technology Inc.
Preliminary
DS41364A-page 109