PIC16F747 Microchip Technology Inc., PIC16F747 Datasheet - Page 41

• Manufacturer Part Number: PIC16F747
• Description: 28/40/44-pin, 8-bit Cmos Flash Microcontrollers With 10-bit A/d And Nanowatt Technology
• Manufacturer: Microchip Technology Inc.

FIGURE 4-6:
4.6.4
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.
 2004 Microchip Technology Inc.
T1OSO
T1OSI
OSC2
OSC1
MODIFYING THE IRCF BITS
Secondary Oscillator
Primary Oscillator
31.25 kHz
PIC16F7X7 CLOCK DIAGRAM
(INTRC)
Oscillator
31.25 kHz
Internal
Source
T1OSCEN
Enable
Oscillator
Block
Sleep
(INTOSC)
8 MHz
31.25 kHz
500 kHz
250 kHz
125 kHz
8 MHz
4 MHz
2 MHz
1 MHz
OSCCON<6:4>
If the IRCF bits are modified while the internal oscillator
is running at any other frequency than INTRC
(31.25 kHz, IRCF<2:0>
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.
111
110
101
100
011
010
001
000
Note:
To Timer1
LP, XT, HS, RC, EC
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 V
specification range; for example:
V
DD
Internal Oscillator
= 2.0V and IRCF = 111 (8 MHz).
CONFIG1 (FOSC2:FOSC0)
T1OSC
SCS<1:0> (T1OSC)
PIC16F7X7
000), there is no need for a
DS30498C-page 39
WDT, FSCM
Peripherals
CPU
DD