PIC16F872_06 Datasheet, PDF (93/168 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS Flash Microcontroller with 10-Bit A/D

PIC16F872
11.3 Reset
The PIC16F872 differentiates between various kinds of
RESET:
• Power-on Reset (POR)
• MCLR Reset during normal operation
• MCLR Reset during SLEEP
• WDT Reset (during normal operation)
• WDT Wake-up (during SLEEP)
• Brown-out Reset (BOR)
Some registers are not affected in any RESET condi-
tion. Their status is unknown on POR and unchanged
in any other RESET. Most other registers are reset to a
“RESET state” on Power-on Reset (POR), on the
MCLR and WDT Reset, on MCLR Reset during
SLEEP, and Brown-out Reset (BOR). They are not
affected by a WDT Wake-up, which is viewed as the
resumption of normal operation. The TO and PD bits
are set or cleared differently in different RESET situa-
tions, as indicated in Table 11-4. These bits are used in
software to determine the nature of the RESET. See
Table 11-6 for a full description of RESET states of all
registers.
A simplified block diagram of the On-Chip Reset circuit
is shown in Figure 11-4.
These devices have a MCLR noise filter in the MCLR
Reset path. The filter will detect and ignore small
pulses.
It should be noted that a WDT Reset does not drive
MCLR pin low.
FIGURE 11-4:
SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT
External
RESET
MCLR
WDT
Module
SLEEP
WDT
Time-out
Reset
VDD Rise
Detect
VDD
Power-on Reset
Brown-out
Reset
S
BODEN
OST/PWRT
OST
10-bit Ripple Counter
R
OSC1
Chip_Reset
Q
(1)
On-Chip
RC OSC
PWRT
10-bit Ripple Counter
Enable PWRT
Enable OST
Note 1: This is a separate oscillator from the RC oscillator of the CLKIN pin.
© 2006 Microchip Technology Inc.
DS30221C-page 91