PIC16F871 Microchip Technology Inc., PIC16F871 Datasheet - Page 93

• Manufacturer Part Number: PIC16F871
• Description: 28/40-pin, 8-bit Cmos Flash Microcontrollers
• Manufacturer: Microchip Technology Inc.

11.3
The PIC16F870/871 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
FIGURE 11-4:
 2003 Microchip Technology Inc.
MCLR
OSC1
V
DD
Note 1: This is a separate oscillator from the RC oscillator of the CLKI pin.
RESET
RC OSC
On-chip
OST/PWRT
Brown-out
V
(1)
Module
Detect
DD
WDT
Reset
Rise
SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT
OST
PWRT
WDT
Time-out
Reset
10-bit Ripple Counter
10-bit Ripple Counter
BOREN
Power-on Reset
External
RESET
SLEEP
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.
PIC16F870/871
S
R
DS30569B-page 91
Q
Enable PWRT
Enable OST
Chip_Reset