PIC16F688
11.4.6
TIME-OUT SEQUENCE
11.4.7
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 configu-
ration and PWRTE bit status. For example, in EC mode
with PWRTE bit erased (PWRT disabled), there will be
no time-out at all. Figure 11.4, Figure 11-5 and
Figure 11-6 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 3.6.2 “Two-Speed Start-up Sequence” and
Section 3.7 “Fail-Safe Clock Monitor”).
The Power Control (PCON) register (address 8Eh) has
two status bits to indicate what type of Reset that last
occurred.
Bit 0 is BOD (Brown-out). BOD is unknown on Power-
on Reset. It must then be set by the user and checked
on subsequent Resets to see if BOD = 0, indicating that
a Brown-out has occurred. The BOD status bit is a
“don’t care” and is not necessarily predictable if the
brown-out circuit is disabled (BODEN<1:0> = 00in the
Configuration Word register).
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).
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 11-5). This is useful for testing purposes or
to synchronize more than one PIC16F688 device
operating in parallel.
For more information, see Section 4.2.3 “Ultra Low-
Power Wake-up” and Section 11.4.4 “Brown-Out
Detect (BOD)”.
Table 11-5 shows the Reset conditions for some
special registers, while Table 11-4 shows the Reset
conditions for all the registers.
TABLE 11-1: TIME-OUT IN VARIOUS SITUATIONS
Power-up
Brown-out Detect
Wake-up
Oscillator Configuration
from Sleep
PWRTE = 0
PWRTE = 1
PWRTE = 0
PWRTE = 1
XT, HS, LP
TPWRT + 1024
• TOSC
1024 • TOSC
TPWRT + 1024
• TOSC
1024 • TOSC
1024 • TOSC
—
RC, EC, INTOSC
TPWRT
—
TPWRT
—
TABLE 11-2: PCON BITS AND THEIR SIGNIFICANCE
POR
BOD
TO
PD
Condition
0
1
u
u
u
0
u
u
1
1
0
0
1
1
u
0
Power-on Reset
Brown-out Detect
WDT Reset
WDT Wake-up
u
u
u
u
u
1
u
0
MCLR Reset during normal operation
MCLR Reset during Sleep
Legend: u= unchanged, x= unknown
TABLE 11-3: SUMMARY OF REGISTERS ASSOCIATED WITH BROWN-OUT
Value on
all other
Resets
Value on
POR, BOD
Address Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(1)
03h
STATUS
PCON
IRP
—
RP1
—
RPO
TO
PD
—
Z
DC
C
0001 1xxx 000q quuu
--01 --qq --0u --uu
8Eh
ULPWUE SBODEN
—
POR
BOD
Legend:
u= unchanged, x= unknown, — = unimplemented bit, reads as ‘0’, q= value depends on condition. Shaded cells are
not used by BOD.
Note 1: Other (non Power-up) Resets include MCLR Reset and Watchdog Timer Reset during normal operation.
2004 Microchip Technology Inc.
Preliminary
DS41203B-page 105
MICROCHIP [ MICROCHIP ]
