PIC18LF452 Microchip Technology, PIC18LF452 Datasheet - Page 27

• Manufacturer Part Number: PIC18LF452
• Description: (PIC18LFxx2) Enhanced FLASH Microcontrollers
• Manufacturer: Microchip Technology

3.0
The PIC18FXXX differentiates between various kinds
of RESET:
a)
b)
c)
d)
e)
f)
g)
h)
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” on Power-on Reset, MCLR, WDT Reset, Brown-
out Reset, MCLR Reset during SLEEP and by the
RESET instruction.
FIGURE 3-1:
2002 Microchip Technology Inc.
MCLR
OSC1
V
Note 1: This is a separate oscillator from the RC oscillator of the CLKI pin.
Power-on Reset (POR)
MCLR Reset during normal operation
MCLR Reset during SLEEP
Watchdog Timer (WDT) Reset (during normal
operation)
Programmable Brown-out Reset (BOR)
RESET Instruction
Stack Full Reset
Stack Underflow Reset
DD
Instruction
RESET
RESET
Pointer
2: See Table 3-1 for time-out situations.
RC OSC
Stack
On-chip
OST/PWRT
Brown-out
V
Module
Detect
(1)
DD
WDT
Reset
Rise
OST
SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT
Stack Full/Underflow Reset
PWRT
External Reset
10-bit Ripple Counter
10-bit Ripple Counter
Time-out
Reset
WDT
BOREN
Power-on Reset
SLEEP
Enable PWRT
Enable OST
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 3-2. These bits
are used in software to determine the nature of the
RESET. See Table 3-3 for a full description of the
RESET states of all registers.
A simplified block diagram of the On-Chip Reset Circuit
is shown in Figure 3-1.
The Enhanced MCU devices have a MCLR noise filter
in the MCLR Reset path. The filter will detect and
ignore small pulses.
The MCLR pin is not driven low by any internal
RESETS, including the WDT.
(2)
PIC18FXX2
S
R
DS39564B-page 25
Q
Chip_Reset