PIC16F627A_05 Datasheet, PDF (104/180 Pages) Microchip Technology – Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC16F627A/628A/648A
14.4.5 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. The total time out will vary based on
oscillator configuration and PWRTE bit Status. For
example, in RC mode with PWRTE bit set (PWRT
disabled), there will be no time out at all. Figure 14-8,
Figure 14-11 and Figure 14-12 depict time out
sequences.
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 14-11). This is useful for testing purposes
or to synchronize more than one PIC16F627A/628A/
648A device operating in parallel.
Table 14-6 shows the Reset conditions for some
special registers, while Table 14-7 shows the Reset
conditions for all the registers.
14.4.6 POWER CONTROL (PCON) STATUS
REGISTER
The PCON/Status register, PCON (address 8Eh), has
two bits.
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 (by
setting BOREN bit = 0 in the Configuration Word).
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 must have occurred (VDD may have
gone too low).
TABLE 14-3: TIME OUT IN VARIOUS SITUATIONS
Oscillator Configuration
Power-up Timer
PWRTE = 0 PWRTE = 1
XT, HS, LP
RC, EC
INTOSC
72 ms +
1024•TOSC
72 ms
72 ms
1024•TOSC
—
—
Brown-out Reset
PWRTE = 0 PWRTE = 1
72 ms +
1024•TOSC
72 ms
72 ms
1024•TOSC
—
—
Wake-up from
Sleep
1024•TOSC
—
6 μs
TABLE 14-4: STATUS/PCON BITS AND THEIR SIGNIFICANCE
POR
BOR
TO
PD
Condition
0
0
0
1
1
1
1
1
Legend:
X
1
1
X
0
X
X
X
0
0
X
X
1
0
u
1
0
0
1
u
u
1
1
0
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
DS40044D-page 102
© 2005 Microchip Technology Inc.