PIC16F631/677/685/687/689/690
14.2.5
TIME-OUT SEQUENCE
14.2.6
POWER CONTROL (PCON)
REGISTER
On power-up, the time-out sequence is as follows: first,
PWRT time-out is invoked after POR has expired, then
OST is activated after the PWRT time-out has expired.
The total time-out will vary based on oscillator
configuration and PWRTE bit status. For example, in
EC mode with PWRTE bit erased (PWRT disabled),
there will be no time-out at all. Figures 14-4, 14-5
and 14-6 depict time-out sequences. The device can
execute code from the INTOSC while OST is active by
enabling Two-Speed Start-up or Fail-Safe Monitor (see
Section 3.7.2 “Two-speed Start-up Sequence” and
Section 3.8 “Fail-Safe Clock Monitor”).
The Power Control register PCON (address 8Eh) has
two Status bits to indicate what type of Reset that last
occurred.
Bit 0 is BOR (Brown-out Reset). BOR is unknown on
Power-on Reset. It must then be set by the user and
checked on subsequent Resets to see if BOR = 0,
indicating that a Brown-out has occurred. The BOR
Status bit is a “don’t care” and is not necessarily
predictable if the brown-out circuit is disabled
(BOREN<1:0> = 00 in the Configuration Word
register).
Since the time-outs occur from the POR pulse, if MCLR
is kept low long enough, the time-outs will expire. Then,
bringing MCLR high will begin execution immediately
(see Figure 14-5). This is useful for testing purposes or
to synchronize more than one PIC16F631/677/685/
687/689/690 device operating in parallel.
Bit 1 is POR (Power-on Reset). It is a ‘0’ on Power-on
Reset and unaffected otherwise. The user must write a
‘1’ to this bit following a Power-on Reset. On a
subsequent Reset, if POR is ‘0’, it will indicate that a
Power-on Reset has occurred (i.e., VDD may have
gone too low).
Table 14-5 shows the Reset conditions for some
special registers, while Table 14-4 shows the Reset
conditions for all the registers.
For more information, see Section 4.2.4 “Ultra Low-
Power Wake-up” and Section 14.2.4 “Brown-out
Reset (BOR)”.
TABLE 14-1: TIME-OUT IN VARIOUS SITUATIONS
Power-up
Brown-out Reset
Wake-up from
Oscillator Configuration
Sleep
PWRTE = 0
PWRTE = 1
PWRTE = 0
PWRTE = 1
XT, HS, LP
TPWRT +
1024 • TOSC
TPWRT +
1024 • TOSC
1024 • TOSC
1024 • TOSC
1024 • TOSC
LP, T1OSCIN = 1
TPWRT
TPWRT
—
—
TPWRT
TPWRT
—
—
—
—
RC, EC, INTOSC
TABLE 14-2: STATUS/PCON BITS AND THEIR SIGNIFICANCE
POR
BOR
TO
PD
Condition
0
u
u
u
u
u
x
0
u
u
u
u
1
1
0
0
u
1
1
1
u
0
u
0
Power-on Reset
Brown-out Reset
WDT Reset
WDT Wake-up
MCLR Reset during normal operation
MCLR Reset during Sleep
Legend: u= unchanged, x= unknown
TABLE 14-3: SUMMARY OF REGISTERS ASSOCIATED WITH BROWN-OUT
Value on
all other
Resets
Value on
POR, BOR
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
PCON
—
—
ULPWUE SBOREN
RPO TO
—
—
Z
POR
DC
BOR
C
--01 --qq
0001 1xxx
--0u --uu
000q quuu
IRP
RP1
PD
STATUS
Legend:
u= unchanged, x= unknown, – = unimplemented bit, reads as ‘0’, q= value depends on condition. Shaded cells are not used by BOR.
Note 1:
Other (non Power-up) Resets include MCLR Reset and Watchdog Timer Reset during normal operation.
© 2007 Microchip Technology Inc.
DS41262D-page 199
MICROCHIP [ MICROCHIP ]
