Datasheet

PIC16C77X
 1999-2013 Microchip Technology Inc. Advance Information DS30275B-page 131
12.3 Reset
The PIC16C77X devices have several different resets.
These resets are grouped into two classifications;
power-up and non-power-up. The power-up type resets
are the power-on and brown-out resets which assume
the device V
DD was below its normal operating range
for the device’s configuration. The non-power up type
resets assume normal operating limits were main-
tained before/during and after the reset.
• Power-on Reset (POR)
• Brown-out Reset (BOR)
•MCLR
reset during normal operation
•MCLR
reset during SLEEP
• WDT Reset (during normal operation)
Some registers are not affected in any reset condition.
Their status is unknown on a power-up reset and
unchanged in any other reset. Most other registers are
placed into an initialized state upon reset, however they
are not affected by a WDT reset during sleep because
this is considered a WDT Wakeup, which is viewed as
the resumption of normal operation.
Several status bits have been provided to indicate
which reset occurred (see Table 12-4). 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 12-5.
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 12-5: SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT
S
R
Q
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 CLKIN pin.
Brown-out
Reset
BODEN
(1)
774.book Page 131 Tuesday, January 29, 2013 12:02 PM