PIC16F616 Microchip Technology Inc., PIC16F616 Datasheet - Page 28

• Manufacturer Part Number: PIC16F616
• Description: 14-pin Flash-based, 8-bit Cmos Microcontrollers
• Manufacturer: Microchip Technology Inc.

PIC16F610/616/16HV610/616
3.2
Clock Source modes can be classified as external or
internal.
• External Clock modes rely on external circuitry for
• Internal clock sources are contained internally
The system clock can be selected between external or
internal clock sources via the FOSC<2:0> bits of the
Configuration Word register.
3.3
3.3.1
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 and the OSC2 is available
for general purpose I/O. Figure 3-2 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
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 3-2:
TABLE 3-1:
DS41288C-page 26
Switch From
Sleep/POR
Sleep/POR
Sleep/POR
Note 1:
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.
within the Oscillator module. The Oscillator
module has two selectable clock frequencies:
4 MHz and 8 MHz
Clock from
Ext. System
Clock Source Modes
External Clock Modes
EC MODE
Alternate pin functions are listed in the
Section 1.0 “Device Overview”.
I/O
OSCILLATOR DELAY EXAMPLES
EXTERNAL CLOCK (EC)
MODE OPERATION
OSC1/CLKIN
OSC2/CLKOUT
Switch To
INTOSC
EC, RC
LP, XT, HS
®
MCU design is fully
PIC
®
MCU
(1)
Preliminary
Frequency
4 MHz to 8 MHz
DC – 20 MHz
32 kHz to 20 MHz
3.3.2
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. When switching between clock sources, a
delay is required to allow the new clock to stabilize.
These oscillator delays are shown in Table 3-1.
OSCILLATOR START-UP TIMER
(OST)
Oscillator Delay
Oscillator Warm-Up Delay (T
2 Instruction Cycles
1024 Clock Cycles (OST)
© 2007 Microchip Technology Inc.
WARM
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