PIC16F87X Datasheet, PDF (125/218 Pages) Microchip Technology – 28/40-pin 8-Bit CMOS FLASH Microcontrollers

PIC16F87X
12.3 RESET
The PIC16F87X 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 12-4. These bits are used in
software to determine the nature of the RESET. See
Table 12-6 for a full description of RESET states of all
registers.
A simplified block diagram of the On-Chip Reset Circuit
is shown in Figure 12-4.
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 12-4:
SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT
External
Reset
MCLR
VDD
OSC1
WDT
Module
VDD Rise
Detect
SLEEP
WDT
Time-out
Reset
Power-on Reset
Brown-out
Reset
BODEN
OST/PWRT
OST
10-bit Ripple Counter
S
Chip_Reset
R
Q
(1)
On-chip
RC OSC
PWRT
10-bit Ripple Counter
Enable PWRT
Note 1: This is a separate oscillator from the RC oscillator of the CLKIN pin.
Enable OST
 2001 Microchip Technology Inc.
DS30292C-page 123