PIC16LC62B datasheet(57/120 Pages) MICROCHIP

57 / 120 page

PIC16C62B/72A

Preliminary

DS35008B-page 57

10.2.3

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 resis-

tor (REXT) and capacitor (CEXT) values, and the operat-

ing temperature. In addition to this, the oscillator

frequency will vary from unit to unit due to normal pro-

cess 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 compo-

nents used. Figure 10-4 shows how the R/C combina-

tion is connected to the PIC16CXXX.

FIGURE 10-4: RC OSCILLATOR MODE

10.3

Reset

The PIC16CXXX 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 by 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 on

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

WDT Wake-up from SLEEP, which is viewed as the

resumption of normal operation. The TO and PD bits

are set or cleared depending on the reset situation, as

indicated in Table 10-4. These bits are used in software

to determine the nature of the reset. See Table 10-6 for

a full description of reset states of all registers.

A simplified block diagram of the on-chip reset circuit is

shown in Figure 10-5.

The PICmicro devices have a MCLR noise filter in the

MCLR reset path. The filter will ignore small pulses.

However, a valid MCLR pulse must meet the minimum

pulse width (TmcL, Specification #30).

No internal reset source (WDT, BOR, POR) willdrive

the MCLR pin low.

OSC2/CLKOUT

Cext

Rext

PIC16CXX

OSC1

Fosc/4

Internal

clock

VDD

VSS

Recommended values:

3 k

Ω ≤ Rext ≤ 100 kΩ

Cext > 20pF

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