PIC16F87-E Datasheet, PDF (40/228 Pages) Microchip Technology – 18/20/28-Pin Enhan lashMicrocontrollers with nanoWatt Technology

PIC16F87/88
4.5.1 INTRC MODES
Using the internal oscillator as the clock source can
eliminate the need for up to two external oscillator pins,
after which it can be used for digital I/O. Two distinct
configurations are available:
• In INTIO1 mode, the OSC2 pin outputs FOSC/4,
while OSC1 functions as RA7 for digital input and
output.
• In INTIO2 mode, OSC1 functions as RA7 and
OSC2 functions as RA6, both for digital input and
output.
4.5.2 OSCTUNE REGISTER
The internal oscillator’s output has been calibrated at the
factory but can be adjusted in the application. This is
done by writing to the OSCTUNE register (Register 4-1).
The tuning sensitivity is constant throughout the tuning
range. The OSCTUNE register has a tuning range of
±12.5%.
When the OSCTUNE register is modified, the INTOSC
and INTRC frequencies will begin shifting to the new fre-
quency. The INTRC clock will reach the new frequency
within 8 clock cycles (approximately 8 * 32 µs = 256 µs);
the INTOSC clock will stabilize within 1 ms. Code execu-
tion continues during this shift. There is no indication that
the shift has occurred. Operation of features that depend
on the 31.25 kHz INTRC clock source frequency, such
as the WDT, Fail-Safe Clock Monitor and peripherals,
will also be affected by the change in frequency.
REGISTER 4-1:
bit 7-6
bit 5-0
OSCTUNE: OSCILLATOR TUNING REGISTER (ADDRESS 90h)
U-0
U-0
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
—
—
TUN5
TUN4
TUN3
TUN2
TUN1
bit 7
R/W-0
TUN0
bit 0
Unimplemented: Read as ‘0’
TUN<5:0>: Frequency Tuning bits
011111 = Maximum frequency
011110 =
•
•
•
000001 =
000000 = Center frequency. Oscillator module is running at the calibrated frequency.
111111 =
•
•
•
100000 = Minimum frequency
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
DS30487C-page 38
 2005 Microchip Technology Inc.