PIC16F506T-ESLASHMCSQTP datasheet(62/116 Pages) MICROCHIP

62 / 116 page

PIC12F510/16F506

DS41268C-page 60

Preliminary

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

capacitance or small external capacitance, the oscilla-

tion frequency can vary dramatically due to changes in

external capacitances, such as PCB trace capacitance

or package lead frame capacitance.

Section 13.0 “Electrical Characteristics”, shows RC

frequency variation from part-to-part due to normal

process variation. The variation is larger for larger val-

ues of R (since leakage current variation will affect RC

frequency more for large R) and for smaller values of C

(since variation of input capacitance will affect RC

frequency more).

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 10-5:

EXTERNAL RC

OSCILLATOR MODE

10.2.5

INTERNAL 4/8 MHz RC

OSCILLATOR

The internal RC oscillator provides a fixed 4/8 MHz

(nominal) system clock (see Section 13.0 “Electrical

Characteristics” for information on variation over

voltage and temperature).

10.2.6

EXTERNAL CLOCK IN

For applications where a clock is already available

elsewhere, users may directly drive the PIC12F510/

16F506 devices provided that this external clock

source meets the AC/DC timing requirements listed in

Section 10.6 “Watchdog Timer (WDT)”. Figure 10-6

below shows how an external clock circuit should be

configured.

FIGURE 10-6:

EXTERNAL CLOCK INPUT

OPERATION

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 uncode protected, regardless of the code-pro-

tect 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 (05h) 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 PIC12F510/16F506 devices, only bits <7:1> of

OSCCAL are implemented. Bits CAL6-CAL0 are used

for calibration. Adjusting CAL6-CAL0 from ‘0000000’

‘1111111’

changes

the

clock

speed.

See

VDD

REXT

CEXT

VSS

OSC1

Internal

clock

FOSC/4

OSC2/CLKOUT

PIC12F510

PIC16F506

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 0 bit of OSCCAL is unimplemented

and should be written as ‘0’ when modify-

ing OSCCAL for compatibility with future

devices.

Clock From

ext. system

OSC2/CLKOUT/RB4

RB5/OSC1/CLKIN

OSC2/CLKOUT/RB4(1)

Clock From

ext. system

OSC2

GP5/OSC1/CLKIN

GP4/OSC2

PIC16F506: EC, HS, XT, LP

PIC12F510: XT, LP

Note 1:

RB4 is available in EC mode only.

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