PIC16F684-ESLASHST datasheet(97/164 Pages) MICROCHIP

97 / 164 page

 2004 Microchip Technology Inc.

Preliminary

DS41202C-page 95

PIC16F684

12.3.1

POWER-ON RESET

The on-chip POR circuit holds the chip in Reset until

VDD has reached a high enough level for proper

operation. To take advantage of the POR, simply

connect the MCLR pin through a resistor to VDD. This

will eliminate external RC components usually needed

to create Power-on Reset. A maximum rise time for

VDD is required. See Section 15.0 “Electrical Specifi-

cations” for details. If the BOD is enabled, the maxi-

mum rise time specification does not apply. The BOD

circuitry will keep the device in Reset until VDD reaches

VBOD

(see

Section 12.3.5

“Brown-Out

Detect

(BOD)”).

When the device starts normal operation (exits the

Reset condition), device operating parameters (i.e.,

voltage, frequency, temperature, etc.) 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.

For additional information, refer to Application Note

AN607, “Power-up Trouble Shooting” (DS00607).

12.3.2

MCLR

PIC16F684 has a 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

MCLR pin low.

The behavior of the ESD protection on the MCLR pin

has been altered from early devices of this family.

Voltages applied to the pin that exceed its specification

can result in both MCLR Resets and excessive current

beyond the device specification during the ESD event.

For this reason, Microchip recommends that the MCLR

pin no longer be tied directly to VDD. The use of an RC

network, as shown in Figure 12-2, is suggested.

An internal MCLR option is enabled by clearing the

MCLRE bit in the Configuration Word register. When

cleared, MCLR is internally tied to VDD and an internal

weak pull-up is enabled for the MCLR pin. In-Circuit

Serial Programming is not affected by selecting the

internal MCLR option.

FIGURE 12-2:

RECOMMENDED MCLR

CIRCUIT

12.3.3

POWER-ON RESET (POR)