PIC16F722A-ESLASHML datasheet(82/284 Pages) MICROCHIP

82 / 284 page

PIC16F/LF722A/723A

DS41417A-page 82

 2010 Microchip Technology Inc.

FIGURE 7-4:

CERAMIC RESONATOR

OPERATION

(XT OR HS MODE)

7.6.4

EXTERNAL RC MODES

The external Resistor-Capacitor (RC) modes support

the use of an external RC circuit. This allows the

designer maximum flexibility in frequency choice while

keeping costs to a minimum when clock accuracy is not

required. There are two modes: RC and RCIO.

In RC mode, the RC circuit connects to OSC1. OSC2/

CLKOUT outputs the RC oscillator frequency divided

by 4. This signal may be used to provide a clock for

external circuitry, synchronization, calibration, test or

other application requirements. Figure 7-5 shows the

external RC mode connections.

FIGURE 7-5:

EXTERNAL RC MODES

In RCIO mode, the RC circuit is connected to OSC1.

OSC2 becomes an additional general purpose I/O pin.

The RC oscillator frequency is a function of the supply

voltage, the resistor (REXT) and capacitor (CEXT) values

and the operating temperature. Other factors affecting

the oscillator frequency are:

• threshold voltage variation

• component tolerances

• packaging variations in capacitance

The user also needs to take into account variation due

to tolerance of external RC components used.

TABLE 7-1:

SUMMARY OF REGISTERS ASSOCIATED WITH CLOCK SOURCES

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.

3: An additional parallel feedback resistor (RP)

may be required for proper ceramic resonator

operation.

C2 Ceramic

RS(1)

OSC1/CLKIN

RF(2)

Sleep

To Internal

Logic

PIC® MCU

RP(3)

Resonator

OSC2/CLKOUT

OSC2/CLKOUT(1)

CEXT

REXT

PIC® MCU

OSC1/CLKIN

FOSC/4 or

Internal

Clock

VDD

VSS

Recommended values: 10 k

  REXT  100 k, <3V

3 k

  REXT  100 k, 3-5V

CEXT > 20 pF, 2-5V

Note 1:

Alternate pin functions are described in

Section 6.1 “Alternate Pin Function”.

Output depends upon RC or RCIO clock mode.

I/O(2)

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value on

POR, BOR

Value on

all other

Resets(1)

CONFIG1(1)

—

MCLRE

PWRTE

WDTE

FOSC2

FOSC1

FOSC0

—

OSCCON

—

IRCF1

IRCF0

ICSL

ICSS

—

--10 qq--

OSCTUNE

—

TUN5

TUN4

TUN3

TUN2

TUN1

TUN0

--00 0000

--uu uuuu

Legend:

x = unknown, u = unchanged, – = unimplemented locations read as ‘0’. Shaded cells are not used by oscillators.

Note 1:

See Configuration Word 1 (Register 8-1) for operation of all bits.

PIC16F722A-E/ML Datasheet(PDF) 82 Page - Microchip Technology

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