PIC12F617T-I/MS データシートの表示（PDF） - Microchip Technology

部品番号

コンポーネント説明

メーカー

PIC12F617T-I/MS

8-Pin Flash-Based, 8-Bit CMOS Microcontrollers

Microchip Technology 

PIC12F609/615/617/12HV609/615

4.2 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 selectable clock frequencies:

4 MHz and 8 MHz

The system clock can be selected between external or

internal clock sources via the FOSC<2:0> bits of the

Configuration Word register.

4.3 External Clock Modes

4.3.1 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. When switching between clock sources, a

delay is required to allow the new clock to stabilize.

These oscillator delays are shown in Table 4-1.

TABLE 4-1:

Switch From

Sleep/POR

Sleep/POR

Sleep/POR

OSCILLATOR DELAY EXAMPLES

Switch To

Frequency

INTOSC

EC, RC

LP, XT, HS

125 kHz to 8 MHz

DC – 20 MHz

32 kHz to 20 MHz

4.3.2 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 and the OSC2 is available

for general purpose I/O. Figure 4-2 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.

Oscillator Delay

Oscillator Warm-Up Delay (TWARM)

2 instruction cycles

1024 Clock Cycles (OST)

FIGURE 4-2:

EXTERNAL CLOCK (EC)

MODE OPERATION

Clock from

Ext. System

I/O

OSC1/CLKIN

PIC® MCU

OSC2/CLKOUT(1)

Note 1: Alternate pin functions are listed in the

Section 1.0 “Device Overview”.

DS41302D-page 38

 2010 Microchip Technology Inc.

Share Link: