PIC16F716 datasheet(60/126 Pages) MICROCHIP

60 / 126 page

PIC16F716

DS41206A-page 58

Preliminary

 2003 Microchip Technology Inc.

9.2.3

RC OSCILLATOR

For timing insensitive applications, the “RC” device

option offers additional cost savings. The RC oscillator

frequency is a function of the supply voltage, the

resistor (REXT) and capacitor (CEXT) values and the

operating temperature. In addition to this, the oscillator

frequency will vary from unit to unit due to normal

process

parameter

variation.

Furthermore,

the

difference in lead frame capacitance between package

types

will

also

affect the

oscillation

frequency,

especially for low CEXT values. The user also needs to

take into account variation due to tolerance of external

R and C components used. Figure 9-3 shows how the

R/C combination is connected to the PIC16F716.

FIGURE 9-3:

RC OSCILLATOR MODE

9.3

Reset

The PIC16F716 differentiates between various kinds of

Reset:

• Power-on Reset (POR)

•MCLR Reset during normal operation

•MCLR Reset during Sleep

• WDT Reset (during normal operation)

• WDT Wake-up (during Sleep)

• Brown-out Reset (BOR)

Some registers are not affected in any Reset condition;

their status is unknown on POR and unchanged in any

other Reset. Most other registers are reset to a “Reset

state” on Power-on Reset (POR), on the MCLR and

WDT Reset, on MCLR Reset during Sleep and Brown-

out Reset (BOR). They are not affected by a WDT

Wake-up, which is viewed as the resumption of normal

operation. The TO and PD bits are set or cleared differ-

ently in different Reset situations as indicated in

Table 9-4. These bits are used in software to determine

the nature of the Reset. See Table 9-6 for a full

description of Reset states of all registers.

A simplified block diagram of the On-chip Reset circuit

is shown in Figure 9-5.

The PICmicro® microcontrollers have an MCLR noise

filter in the MCLR Reset path. The filter will detect and

ignore small pulses.

It should be noted that a WDT Reset does not drive the

MCLR pin low.

9.4

Power-On Reset (POR)

A Power-on Reset pulse is generated on-chip when

VDD rise is detected. To take advantage of the POR,

just tie the MCLR pin directly (or through a resistor) to

VDD. This will eliminate external RC components

usually needed to create a Power-on Reset. A

maximum rise time for VDD is specified (parameter

D004). For a slow rise time, see Figure 9-4.

When the device starts normal operation (exits the

Reset

condition),

device

operating

parameters

(voltage, frequency, temperature,...) must be met to

ensure operation. If these conditions are not met, the

device must be held in Reset until the operating

conditions are met. Brown-out Reset may be used to

meet the start-up conditions.

FIGURE 9-4:

EXTERNAL POWER-ON

RESET CIRCUIT (FOR

SLOW VDD POWER-UP)

OSC2/CLKOUT

CEXT

REXT

PIC16F716

OSC1

FOSC/4

Internal

clock

VDD

VSS

Recommended values:

Ω ≤ REXT ≤ 100 kΩ (VDD ≥ 3.0V)

10 k

Ω ≤ REXT ≤ 100 kΩ (VDD ≥ 3.0V)

CEXT

> 20 pF

Note

External Power-on Reset circuit is required

only if VDD power-up slope is too slow. The

diode D helps discharge the capacitor quickly

when VDD powers down.

R < 40 k

Ω is recommended to make sure that

voltage drop across R does not violate the

device’s electrical specification.

R1 = 100

Ω to 1 kΩ will limit any current

flowing into MCLR from external capacitor C

in the event of MCLR/VPP pin breakdown due

to Electrostatic Discharge (ESD) or Electrical

Overstress

(EOS).

VDD

MCLR

PIC16F716

VDD

PIC16F716 Datasheet(PDF) 60 Page - Microchip Technology

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