PIC16F570 datasheet(41/134 Pages) MICROCHIP

41 / 134 page

 2012-2014 Microchip Technology Inc.

DS40001652C-page 41

PIC16F527

Also, see the Electrical Specifications section for

variation of oscillator frequency due to VDD for given

REXT/CEXT values, as well as frequency variation due

to operating temperature for given R, C and VDD

values.

FIGURE 8-5:

EXTERNAL RC

OSCILLATOR MODE

8.3.5

INTERNAL 4/8 MHz RC

OSCILLATOR

The internal RC oscillator provides a fixed 4/8 MHz

(nominal) system clock at VDD = 5V and 25°C, (see

Section 15.0

“Electrical

Characteristics”

for

information on variation over voltage and temperature).

In addition, a calibration instruction is programmed into

the last address of memory, which contains the calibra-

tion value for the internal RC oscillator. This location is

always non-code protected, regardless of the code-

protect settings. This value is programmed as a MOVLW

XX instruction where XX is the calibration value, and is

placed at the Reset vector. This will load the W register

with the calibration value upon Reset and the PC will

then roll over to the users program at address 0x000.

The user then has the option of writing the value to the

OSCCAL Register or ignoring it.

OSCCAL, when written to with the calibration value, will

“trim” the internal oscillator to remove process variation

from the oscillator frequency.

For the PIC16F527 device, only bits <7:1> of OSCCAL

are used for calibration. See Register 4-3 for more

information.

VDD

REXT

CEXT

VSS

OSC1

Internal

clock

FOSC/4

OSC2/CLKOUT

PIC® Device

Note:

Erasing the device will also erase the pre-

programmed internal calibration value for

the internal oscillator. The calibration

value must be read prior to erasing the

part so it can be reprogrammed correctly

later.

Note:

The bit 0 of the OSCCAL register is

unimplemented and should be written as

‘0’

when

modifying

OSCCAL

for

compatibility with future devices.

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