PIC12F635ESLASHPQTP datasheet(33/196 Pages) MICROCHIP

33 / 196 page

Preliminary

DS41232B-page 31

PIC12F635/PIC16F636/639

3.3.2

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 pin and the RA5 pin 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 PIC12F635/PIC16F636/639

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 3-2:

EXTERNAL CLOCK (EC)

MODE OPERATION

3.3.3

LP, XT, HS MODES

The LP, XT and HS modes support the use of quartz

crystal resonators or ceramic resonators connected to

the OSC1 and OSC2 pins (Figure 3-1). The mode

selects a low, medium or high gain setting of the

internal inverter-amplifier to support various resonator

types and speed.

LP Oscillator mode selects the lowest gain setting of

the

internal

inverter-amplifier.

mode

current

consumption is the least of the three modes. This mode

is best suited to drive resonators with a low drive level

specification, for example, tuning fork type crystals.

XT Oscillator mode selects the intermediate gain

setting of the internal inverter-amplifier. XT mode

current consumption is the medium of the three modes.

This mode is better suited to drive resonators with a

medium drive level specification, for example, low-

frequency AT-cut quartz crystal resonators.

HS Oscillator mode selects the highest gain setting of

the

internal

inverter-amplifier.

mode

current

consumption is the highest of the three modes. This

mode is better suited for resonators that require a high

drive setting, for example, high-frequency AT-cut

quartz crystal resonators or ceramic resonators.

Figure 3-3 and Figure 3-4 show typical circuits for

quartz crystal and ceramic resonators, respectively.

FIGURE 3-3:

QUARTZ CRYSTAL

OPERATION (LP, XT OR

HS MODE)

FIGURE 3-4:

CERAMIC RESONATOR

OPERATION

(XT OR HS MODE)

OSC1/CLKIN

I/O (OSC2)

RA4

Clock from

Ext. System

PIC12F635/PIC16F636/639

Note 1: Quartz

crystal

characteristics

vary

according

type,

package

and

manufacturer. The user should consult the

manufacturer data sheets for specifications

and recommended application.

2: Always verify oscillator performance over

the VDD and temperature range that is

expected for the application.

Note 1:

A series resistor (RS) may be required for

quartz crystals with low drive level.

The value of RF varies with the Oscillator

mode selected (typically between 2 M

Ω to

10 M

Ω).

Quartz

OSC2

RS(1)

OSC1

RF(2)

Sleep

PIC12F635/PIC16F636/639

Crystal

To Internal

Logic

Note

1: A series resistor (RS) may be required for

ceramic resonators with low drive level.

2: The value of RF varies with the Oscillator

mode selected (typically between 2 M

Ω to

10 M

Ω).

3: An additional parallel feedback resistor (RP)

may be required for proper ceramic resonator

operation (typical value 1 M

Ω).

C2 Ceramic

OSC2

RS(1)

OSC1

RP(3)

Resonator

RF(2)

Sleep

PIC12F635/PIC16F636/639

To Internal

Logic

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