Datasheet

© 2009 Microchip Technology Inc. DS41203E-page 115
PIC16F688
11.2.5 TIME-OUT SEQUENCE
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 11.2.1, 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 3.7.2 “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 11-5). This is useful for testing purposes or
to synchronize more than one PIC16F688 device
operating in parallel.
Table 11-5 shows the Reset conditions for some
special registers, while Table 11-4 shows the Reset
conditions for all the registers.
11.2.6 POWER CONTROL (PCON)
REGISTER
The Power Control (PCON) register (address 8Eh) has
two Status bits to indicate what type of Reset that last
occurred.
Bit 0 is BO
R (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
subsequent Reset, if POR
is ‘0’, it will indicate that a
Power-on Reset has occurred (i.e., V
DD may have
gone too low).
For more information, see Section 4.2.4 “Ultra
Low-Power Wake-up” and Section 11.2.4
“Brown-Out Reset (BOR)”.
TABLE 11-1: TIME-OUT IN VARIOUS SITUATIONS
TABLE 11-2: PCON BITS AND THEIR SIGNIFICANCE
TABLE 11-3: SUMMARY OF REGISTERS ASSOCIATED WITH BROWN-OUT RESET
Oscillator Configuration
Power-up Brown-out Reset
Wake-up
from Sleep
PWRTE
= 0 PWRTE = 1 PWRTE = 0 PWRTE = 1
XT, HS, LP TPWRT + 1024
• T
OSC
1024 • TOSC TPWRT + 1024
• T
OSC
1024 • TOSC 1024 • TOSC
RC, EC, INTOSC TPWRT —TPWRT ——
POR
BOR TO PD Condition
0u11Power-on Reset
1011Brown-out Reset
uu0uWDT Reset
uu00WDT Wake-up
uuuuMCLR
Reset during normal operation
uu10MCLR Reset during Sleep
Legend: u = unchanged, x = unknown
Name Bit 9 Bit 8 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)
CONFIG
(2)
BOREN1 BOREN0 CPD CP MCLRE PWRTE WDTE FOSC2 FOSC1 FOSC0 — —
PCON
— — ULPWUE SBOREN — —PORBOR --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.
2: See Configuration Word register (Register 11-1) for operation of all register bits.