PIC18F2X1X/4X1X
DS39636D-page 50
2009 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
RI
TO
PD
POR BOR STKFUL
STKUNF
Power-on Reset
0000h
1
111
00
0
RESET instruction
0000h
u(2)
0uu
uu
u
Brown-out Reset
0000h
u(2)
111
u0
u
MCLR during power-managed
Run modes
0000h
u(2)
u1u
uu
u
MCLR during power-managed
Idle modes and Sleep mode
0000h
u(2)
u10
uu
u
WDT time-out during full power
or power-managed Run mode
0000h
u(2)
u0u
uu
u
MCLR during full power
execution
0000h
u(2)
uuu
uu
u
Stack Full Reset (STVREN = 1)
0000h
u(2)
uuu
uu
1
u
Stack Underflow Reset
(STVREN = 1)
0000h
u(2)
uuu
uu
u
1
Stack Underflow Error (not an
actual Reset, STVREN = 0)
0000h
u(2)
uuu
uu
u
1
WDT Time-out during
power-managed Idle or Sleep
modes
PC + 2
u(2)
u00
uu
u
Interrupt exit from
power-managed modes
PC + 2(1)
u(2)
uu0
uu
u
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).
2:
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’.