PIC16F570 datasheet(41/129 Pages) MICROCHIP

41 / 129 page

 2013-2014 Microchip Technology Inc.

DS40001684E-page 41

PIC16F570

Figure 8-5 shows how the R/C combination is

connected to the PIC16F570 device. For REXT values

below 3.0 k

, the oscillator operation may become

unstable or stop completely. For very high REXT values

(e.g., 1 M

), the oscillator becomes sensitive to noise,

humidity and leakage. Thus, we recommend keeping

REXT between 5.0 k

 and 100 k.

Although the oscillator will operate with no external

capacitor (CEXT = 0 pF), we recommend using values

above 20 pF for noise and stability reasons. With no

external capacitance or with values below 20 pF, the

oscillation frequency can vary dramatically due to

changes in external capacitances, such as PCB trace

capacitance or package lead frame capacitance.

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 overvoltage and temperature).

In addition, a calibration instruction is programmed into

the last address of memory, which contains the

calibration 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 PIC16F570 device, only bits <7:1> of OSCCAL

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

information.

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.

VDD

REXT

CEXT

VSS

OSC1

Internal

clock

FOSC/4

OSC2/CLKOUT

PIC® Device

PIC16F570 Datenblatt(PDF) 41 Page - Microchip Technology

PIC16F570 Datenblatt(HTML) 41 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datenblatt Download

Link URL