Datasheet

PIC16F87/88
DS30487D-page 134  2002-2013 Microchip Technology Inc.
15.8 Time-out Sequence
On power-up, the time-out sequence is as follows: the
PWRT delay starts (if enabled) when a POR occurs.
Then, OST starts counting 1024 oscillator cycles when
PWRT ends (LP, XT, HS). When the OST ends, the
device comes out of Reset.
If MCLR
is kept low long enough, all delays will expire.
Bringing MCLR
high will begin execution immediately.
This is useful for testing purposes, or to synchronize
more than one PIC16F87/88 device operating in
parallel.
Table 15-3 shows the Reset conditions for the
STATUS, PCON and PC registers, while Table 15-4
shows the Reset conditions for all the registers.
15.9 Power Control/Status Register
(PCON)
The Power Control/Status Register, PCON, has two
bits to indicate the type of Reset that last occurred.
Bit 0 is Brown-out Reset Status bit, BOR. Bit BOR is
unknown on a Power-on Reset. It must then be set by
the user and checked on subsequent Resets to see if
bit BOR
cleared, indicating a Brown-out Reset
occurred. When the Brown-out Reset is disabled, the
state of the BOR
bit is unpredictable.
Bit 1 is POR
(Power-on Reset Status bit). It is cleared
on a Power-on Reset and unaffected otherwise. The
user must set this bit following a Power-on Reset.
TABLE 15-1: TIME-OUT IN VARIOUS SITUATIONS
TABLE 15-2: STATUS BITS AND THEIR SIGNIFICANCE
Oscillator
Configuration
Power-up Brown-out Reset
Wake-up from
Sleep
PWRTE
= 0 PWRTE = 1 PWRTE = 0 PWRTE = 1
XT, HS, LP T
PWRT + 1024 • TOSC 1024 • TOSC TPWRT + 1024 • TOSC 1024 • TOSC 1024 • TOSC
EXTRC, INTRC TPWRT 5-10 s
(1)
TPWRT 5-10 s
(1)
5-10 s
(1)
T1OSC ————5-10s
(1)
Note 1: CPU start-up is always invoked on POR, BOR and wake-up from Sleep. The 5-10 s delay is based on a
1 MHz system clock.
POR BOR TO PD
0x11Power-on Reset
0x0xIllegal, TO
is set on POR
0xx0Illegal, PD is set on POR
1011Brown-out Reset
1101WDT Reset
1100WDT Wake-up
11uuMCLR
Reset during Normal Operation
1110MCLR
Reset during Sleep or Interrupt Wake-up from Sleep
Legend: u = unchanged, x = unknown