Datasheet

 2001-2013 Microchip Technology Inc. DS39582C-page 147
PIC16F87XA
14.3 Reset
The PIC16F87XA 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 condition.
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 differ-
ently in different Reset situations as indicated in
Table 14-4. These bits are used in software to deter-
mine the nature of the Reset. See Table 14-6 for a full
description of Reset states of all registers.
A simplified block diagram of the on-chip Reset circuit
is shown in Figure 14-4.
FIGURE 14-4: SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT
S
RQ
External
Reset
MCLR
VDD
OSC1
WDT
Module
V
DD Rise
Detect
OST/PWRT
On-chip
RC OSC
WDT
Time-out
Power-on Reset
OST
10-bit Ripple Counter
PWRT
Chip_Reset
10-bit Ripple Counter
Reset
Enable OST
Enable PWRT
Sleep
Note 1: This is a separate oscillator from the RC oscillator of the CLKI pin.
Brown-out
Reset
BODEN
(1)