PIC16F87-E Datasheet, PDF (136/228 Pages) Microchip Technology – 18/20/28-Pin Enhan lashMicrocontrollers with nanoWatt Technology

PIC16F87/88
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
Oscillator
Configuration
Power-up
PWRTE = 0
PWRTE = 1
Brown-out Reset
PWRTE = 0
PWRTE = 1
Wake-up from
Sleep
XT, HS, LP
TPWRT + 1024 • TOSC
EXTRC, INTRC
TPWRT
T1OSC
—
1024 • TOSC
5-10 µs⁽¹⁾
—
TPWRT + 1024 • TOSC
TPWRT
—
1024 • TOSC
5-10 µs⁽¹⁾
—
1024 • TOSC
5-10 µs⁽¹⁾
5-10 µs⁽¹⁾
Note 1: CPU start-up is always invoked on POR, BOR and wake-up from Sleep. The 5-10 µs delay is based on a
1 MHz system clock.
TABLE 15-2: STATUS BITS AND THEIR SIGNIFICANCE
POR
BOR
TO
PD
0
x
1
1
0
x
0
x
0
x
x
0
1
0
1
1
1
1
0
1
1
1
0
0
1
1
u
u
1
1
1
0
Legend: u = unchanged, x = unknown
Power-on Reset
Illegal, TO is set on POR
Illegal, PD is set on POR
Brown-out Reset
WDT Reset
WDT Wake-up
MCLR Reset during Normal Operation
MCLR Reset during Sleep or Interrupt Wake-up from Sleep
DS30487C-page 134
 2005 Microchip Technology Inc.