PIC16F7X7 datasheet(41/276 Pages) MICROCHIP

41 / 276 page

 2004 Microchip Technology Inc.

DS30498C-page 39

PIC16F7X7

FIGURE 4-6:

PIC16F7X7 CLOCK DIAGRAM

4.6.4

MODIFYING THE IRCF BITS

The IRCF bits can be modified at any time regardless of

which clock source is currently being used as the

system clock. The internal oscillator allows users to

change the frequency during run time. This is achieved

by modifying the IRCF bits in the OSCCON register.

The sequence of events that occur after the IRCF bits

are modified is dependent upon the initial value of the

IRCF bits before they are modified. If the INTRC

(31.25 kHz, IRCF<2:0> = 000) is running and the IRCF

bits are modified to any other value than ‘000’, a 4 ms

(approx.) clock switch delay is turned on. Code execu-

tion continues at a higher than expected frequency

while the new frequency stabilizes. Time sensitive code

should wait for the IOFS bit in the OSCCON register to

become set before continuing. This bit can be

monitored to ensure that the frequency is stable before

using the system clock in time critical applications.

If the IRCF bits are modified while the internal oscillator

is running at any other frequency than INTRC

(31.25 kHz, IRCF<2:0>

≠ 000), there is no need for a

4 ms (approx.) clock switch delay. The new INTOSC

frequency will be stable immediately after the eight

falling edges. The IOFS bit will remain set after clock

switching occurs.

Secondary Oscillator

T1OSCEN

Enable

Oscillator

T1OSO

T1OSI

OSC1

OSC2

Sleep

Primary Oscillator

LP, XT, HS, RC, EC

T1OSC

CPU

Peripherals

8 MHz

4 MHz

2 MHz

1 MHz

500 kHz

125 kHz

250 kHz

OSCCON<6:4>

111

110

101

100

011

010

001

000

31.25 kHz

Source

Internal

Oscillator

Block

WDT, FSCM

31.25 kHz

8 MHz

Internal Oscillator

(INTRC)

(INTOSC)

CONFIG1 (FOSC2:FOSC0)

SCS<1:0> (T1OSC)

To Timer1

Note:

Caution must be taken when modifying the

IRCF bits using BCF or BSF instructions. It

is possible to modify the IRCF bits to a

frequency that may be out of the VDD

specification range; for example:

VDD = 2.0V and IRCF = 111 (8 MHz).

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