PIC876 datasheet(125/218 Pages) MICROCHIP

125 / 218 page

 2001 Microchip Technology Inc.

DS30292C-page 123

PIC16F87X

12.3

RESET

The PIC16F87X 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 condi-

tion. 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 differently in different RESET situa-

tions as indicated in Table 12-4. These bits are used in

software to determine the nature of the RESET. See

Table 12-6 for a full description of RESET states of all

registers.

A simplified block diagram of the On-Chip Reset Circuit

is shown in Figure 12-4.

These devices have a 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

MCLR pin low.

FIGURE 12-4:

SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT

External

Reset

MCLR

VDD

OSC1

WDT

Module

VDD Rise

Detect

OST/PWRT

On-chip

RC OSC

WDT

Time-out

Power-on Reset

OST

10-bit Ripple Counter

PWRT

Chip_Reset

10-bit Ripple Counter

Reset

Enable OST

Enable PWRT

SLEEP

Note 1: This is a separate oscillator from the RC oscillator of the CLKIN pin.

Brown-out

Reset

BODEN

(1)

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