PIC16F636T-I/SL(2005) View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16F636T-I/SL
(Rev.:2005)

8/14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

Microchip Technology 

PIC12F635/PIC16F636/639

3.2 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 modules (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

PIC12F635/PIC16F636/639. The device has two inter-

nal oscillators: the 8 MHz High-Frequency Internal

Oscillator (HFINTOSC) and 31 kHz Low-Frequency

Internal Oscillator (LFINTOSC).

The system clock can be selected between external or

internal clock sources via the System Clock Selection

(SCS) bit (see Section 3.5 “Clock Switching”).

3.3 External Clock Modes

3.3.1 OSCILLATOR START-UP TIMER (OST)

If the PIC12F635/PIC16F636/639 is configured for LP,

XT or HS modes, the Oscillator Start-up Timer (OST)

counts 1024 oscillations from the OSC1 pin following a

Power-on Reset (POR) and 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 PIC12F635/

PIC16F636/639.

When switching between clock sources, a delay is

required to allow the new clock to stabilize. Table 3-1

shows oscillator delay examples.

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 3.6 “Two-Speed

Clock Start-up Mode”).

TABLE 3-1: OSCILLATOR DELAY EXAMPLES

Switch From

Switch To

Frequency

Sleep/POR

Sleep/POR

LFINTOSC (31 kHz)

Sleep/POR

LFINTOSC

HFINTOSC

EC, RC

EC, RC

LP, XT, HS

31 kHz

125 kHz-8 MHz

DC – 20 MHz

DC – 20 MHz

31 kHz-20 MHz

LFINTOSC (31 kHz)

HFINTOSC

125 kHz-8 MHz

Oscillator Delay

5 μs-10 μs (approx.)

CPU Start-up

1024 Clock Cycles (OST)

1 μs (approx.)

DS41232B-page 30

Preliminary

© 2005 Microchip Technology Inc.

Share Link: