PIC16F84A-04E/SS【PDF 19/81 页】IC MCU CMOS 4MHZ 1K FLASH 20SSOP

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PIC16F84A

DS35007B-page 24

2001 Microchip Technology Inc.

6.3

RESET

The PIC16F84A differentiates between various kinds

of RESET:

Power-on Reset (POR)

MCLR during normal operation

MCLR during SLEEP

WDT Reset (during normal operation)

WDT Wake-up (during SLEEP)

Figure 6-4 shows a simplified block diagram of the

On-Chip RESET Circuit. The MCLR Reset path has a

noise filter to ignore small pulses. The electrical speci-

fications state the pulse width requirements for the

MCLR pin.

Some registers are not affected in any RESET condition;

their status is unknown on a POR and unchanged in any

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

state” on POR, MCLR or WDT Reset during normal oper-

ation and on MCLR during SLEEP. They are not affected

by a WDT Reset during SLEEP, since this RESET is

viewed as the resumption of normal operation.

Table 6-3 gives a description of RESET conditions for

the program counter (PC) and the STATUS register.

Table 6-4 gives a full description of RESET states for all

registers.

The TO and PD bits are set or cleared differently in dif-

ferent RESET situations (Section 6.7). These bits are

used in software to determine the nature of the RESET.

FIGURE 6-4:

SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT

TABLE 6-3:

RESET CONDITION FOR PROGRAM COUNTER AND THE STATUS REGISTER

External Reset

MCLR

VDD

OSC1/

WDT

Module

VDD Rise

Detect

OST/PWRT

On-Chip

RC Osc(1)

WDT

Time-out

Power-on Reset

OST

10-bit Ripple Counter

PWRT

Chip_Reset

10-bit Ripple Counter

Reset

Enable OST

Enable PWRT

SLEEP

CLKIN

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

2: See Table 6-5.

See Table 6-5

Condition

Program Counter

STATUS Register

Power-on Reset

000h

0001 1xxx

MCLR during normal operation

000h

000u uuuu

MCLR during SLEEP

000h

0001 0uuu

WDT Reset (during normal operation)

000h

0000 1uuu

WDT Wake-up

PC + 1

uuu0 0uuu

Interrupt wake-up from SLEEP

PC + 1(1)

uuu1 0uuu

Legend: u = unchanged, x = unknown

Note 1: When the wake-up is due to an interrupt and the GIE bit is set, the PC is loaded with the interrupt vector (0004h).

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