Microchip Technology AC244045 Data Sheet
PIC16F72X/PIC16LF72X
DS41341E-page 38
© 2009 Microchip Technology Inc.
3.6
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 = 1 (PWRT disabled), there will be no
time-out at all. Figure 3-4, Figure 3-5 and Figure 3-6
depict time-out sequences.
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 = 1 (PWRT disabled), there will be no
time-out at all. Figure 3-4, Figure 3-5 and Figure 3-6
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 3-5). This is useful for testing purposes or
to synchronize more than one PIC16F72X/
PIC16LF72X device operating in parallel.
is kept low long enough, the time-outs will expire. Then,
bringing MCLR high will begin execution immediately
(see Figure 3-5). This is useful for testing purposes or
to synchronize more than one PIC16F72X/
PIC16LF72X device operating in parallel.
Table 3-3 shows the Reset conditions for some special
registers.
registers.
3.7
Power Control (PCON) Register
The Power Control (PCON) register has two Status bits
to indicate what type of Reset that last occurred.
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).
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
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 3.5 “Brown-Out
Reset (BOR)”.
Reset (BOR)”.
TABLE 3-2:
TIME-OUT IN VARIOUS SITUATIONS
TABLE 3-3:
RESET BITS AND THEIR SIGNIFICANCE
Oscillator Configuration
Power-up
Brown-out Reset
Wake-up from
Sleep
PWRTE = 0
PWRTE = 1
PWRTE = 0
PWRTE = 1
XT, HS, LP
(1)
T
PWRT
+ 1024 •
T
OSC
1024 • T
OSC
T
PWRT
+ 1024 •
T
OSC
1024 • T
OSC
1024 • T
OSC
RC, EC, INTOSC
T
PWRT
—
T
PWRT
—
—
Note 1:
LP mode with T1OSC disabled.
POR
BOR
TO
PD
Condition
0
u
1
1
Power-on Reset
1
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