PIC16F684_07 Datasheet, PDF (104/192 Pages) Microchip Technology – 14-Pin, Flash-Based 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC16F684
12.3.6 TIME-OUT SEQUENCE
On power-up, the time-out sequence is as follows:
• PWRT time-out is invoked after POR has expired.
• 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. Figure 12-4, Figure 12-5 and
Figure 12-6 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”).
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 12-5). This is useful for testing purposes or
to synchronize more than one PIC16F684 device
operating in parallel.
Table 12-5 shows the Reset conditions for some
special registers, while Table 12-4 shows the Reset
conditions for all the registers.
12.3.7 POWER CONTROL (PCON)
REGISTER
The Power Control register PCON (address 8Eh) has
two Status bits to indicate what type of Reset occurred
last.
Bit 0 is BOR (Brown-out). 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).
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 subse-
quent Reset, if POR is ‘0’, it will indicate that a
Power-on Reset has occurred (i.e., VDD may have
gone too low).
For more information, see Section 4.2.4 “Ultra
Low-Power Wake-up” and Section 12.3.4
“Brown-Out Reset (BOR)”.
TABLE 12-1: TIME-OUT IN VARIOUS SITUATIONS
Oscillator Configuration
Power-up
PWRTE = 0
PWRTE = 1
XT, HS, LP
RC, EC, INTOSC
TPWRT + 1024 •
TOSC
TPWRT
1024 • TOSC
—
Brown-out Reset
PWRTE = 0
TPWRT + 1024 •
TOSC
TPWRT
PWRTE = 1
1024 • TOSC
—
Wake-up from
Sleep
1024 • TOSC
—
TABLE 12-2: STATUS/PCON BITS AND THEIR SIGNIFICANCE
POR
BOR
TO
PD
Condition
0
x
1
1
Power-on Reset
u
0
1
1
Brown-out Reset
u
u
0
u
WDT Reset
u
u
0
0
WDT Wake-up
u
u
u
u
MCLR Reset during normal operation
u
u
1
0
MCLR Reset during Sleep
Legend: u = unchanged, x = unknown
TABLE 12-3: SUMMARY OF REGISTERS ASSOCIATED WITH BROWN-OUT RESET
Name Bit 7 Bit 6 Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on:
POR, BOR
Value on
all other
Resets⁽¹⁾
PCON
—
— ULPWUE SBOREN —
— POR BOR --01 --qq --0u --uu
STATUS IRP RP1
RP0
TO
PD
Z
DC
C 0001 1xxx 000q quuu
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.
DS41202F-page 102
© 2007 Microchip Technology Inc.