PIC18F4520ESLASHMLSTQP datasheet(50/390 Pages) MICROCHIP

50 / 390 page

PIC18F2420/2520/4420/4520

DS39631A-page 48

Preliminary

 2004 Microchip Technology Inc.

4.6

Reset State of Registers

Most registers are unaffected by a Reset. Their status

is unknown on POR and unchanged by all other

Resets. The other registers are forced to a “Reset

state” depending on the type of Reset that occurred.

Most registers are not affected by a WDT wake-up,

since this is viewed as the resumption of normal oper-

ation. Status bits from the RCON register, RI, TO, PD,

POR and BOR, are set or cleared differently in different

Reset situations, as indicated in Table 4-3. These bits

are used in software to determine the nature of the

Reset.

Table 4-4 describes the Reset states for all of the

Special Function Registers. These are categorized by

Power-on and Brown-out Resets, Master Clear and

WDT Resets and WDT wake-ups.

TABLE 4-3:

STATUS BITS, THEIR SIGNIFICANCE AND THE INITIALIZATION CONDITION

FOR RCON REGISTER

Condition

Program

Counter

RCON Register

STKPTR Register

SBOREN

POR BOR

STKFUL

STKUNF

Power-on Reset

0000h

111

RESET

Instruction

0000h

u(2)

0uu

Brown-out Reset

0000h

u(2)

111

MCLR during Power Managed

Run Modes

0000h

u(2)

u1u

MCLR during Power Managed

Idle Modes and Sleep Mode

0000h

u(2)

u10

WDT Time-out during Full Power

or Power Managed Run Mode

0000h

u(2)

u0u

MCLR during Full Power

Execution

0000h

u(2)

uuu

Stack Full Reset (STVREN = 1)

0000h

u(2)

uuu

Stack Underflow Reset

(STVREN = 1)

0000h

u(2)

uuu

Stack Underflow Error (not an

actual Reset, STVREN = 0)

0000h

u(2)

uuu

WDT Time-out during Power

Managed Idle or Sleep Modes

PC + 2

u(2)

u00

Interrupt Exit from Power

Managed Modes

PC + 2(1)

u(2)

uu0

Legend: u = unchanged

Note 1:

When the wake-up is due to an interrupt and the GIEH or GIEL bits are set, the PC is loaded with the

interrupt vector (008h or 0018h).

Reset state is ‘1’ for POR and unchanged for all other Resets when software BOR is enabled

(BOREN1:BOREN0 configuration bits = 01 and SBOREN = 1). Otherwise, the Reset state is ‘0’.

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