PIC18C242 MICROCHIP [Microchip Technology], PIC18C242 Datasheet - Page 23

• Manufacturer Part Number: PIC18C242
• Description: High-Performance Microcontrollers with 10-Bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

3.0
The PIC18CXXX 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
FIGURE 3-1:
Note 1: This is a separate oscillator from the RC oscillator of the CLKIN pin.
7/99 Microchip Technology Inc.
MCLR
OSC1
V
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
2: See Table 3-1 for time-out situations.
RESET
RESET
Pointer
RC OSC
Stack
On-chip
OST/PWRT
Brown-out
V
Module
SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT
detect
WDT
DD
Reset
(1)
Stack Full/Underflow Reset
rise
OST
PWRT
10-bit Ripple counter
WDT
Time-out
Reset
10-bit Ripple counter
External Reset
BOREN
Power-on Reset
SLEEP
Preliminary
Enable PWRT
Enable OST
Power-on Reset, MCLR, WDT reset, Brown-out Reset,
MCLR reset during SLEEP and by the RESET instruc-
tion.
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.
A WDT reset does not drive MCLR pin low.
(2)
PIC18CXX2
S
R
DS39026B-page 23
Q
Chip_Reset