PIC18F1220 MICROCHIP [Microchip Technology], PIC18F1220 Datasheet - Page 35

• Manufacturer Part Number: PIC18F1220
• Description: 18/20/28-Pin High-Performance, Enhanced Flash Microcontrollers with 10-bit A/D and nanoWatt Technology
• Manufacturer: MICROCHIP [Microchip Technology]

4.0
The PIC18F1220/1320 devices differentiate 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”, depending on the type of Reset that occurred.
FIGURE 4-1:
 2004 Microchip Technology Inc.
OSC1
MCLR
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
execution)
Programmable Brown-out Reset (BOR)
RESET Instruction
Stack Full Reset
Stack Underflow Reset
DD
RESET
Instruction
2: See Table 4-1 for time-out situations.
INTRC
RESET
OST/PWRT
Pointer
32 s
Stack
( )_IDLE
Brown-out
V
Time-out
(1)
Sleep
DD
Detect
WDT
Reset
Rise
OST
SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT
PWRT
Stack Full/Underflow Reset
External Reset
MCLRE
10-bit Ripple Counter
11-bit Ripple Counter
POR Pulse
BOR
1024 Cycles
65.5 ms
Most registers are not affected by a WDT wake-up,
since this is viewed as the resumption of normal
operation. Status bits from the RCON register
(Register 4-1), RI, TO, PD, POR and BOR, are set or
cleared differently in different Reset situations, as
indicated in Table 4-2. These bits are used in software
to determine the nature of the Reset. See Table 4-3 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 4-1.
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.
The MCLR input provided by the MCLR pin can be
disabled with the MCLRE bit in Configuration
Register 3H (CONFIG3H<7>).
PIC18F1220/1320
S
R
DS39605C-page 33
Q
Enable OST
Enable PWRT
Chip_Reset
(2)