Datasheet

PIC16C77X
 1999-2013 Microchip Technology Inc. Advance Information DS30275B-page 133
12.8 Time-out Sequence
On power-up the time-out sequence is as follows: First
PWRT time-out is invoked by the POR pulse. When the
PWRT delay expires the Oscillator Start-up Timer is
activated. The total time-out will vary based on oscilla-
tor configuration and the status of the PWRT. For exam-
ple, in RC mode with the PWRT disabled, there will be
no time-out at all. Figure 12-7, Figure 12-8, Figure 12-
9 and Figure 12-10 depict time-out sequences on
power-up.
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
(Figure 12-9). This is useful for testing purposes or to
synchronize more than one PICmicro microcontroller
operating in parallel.
Table 12 - 5 shows the reset conditions for some special
function registers, while Table 12-6 shows the reset
conditions for all the registers.
12.9 Power Control/Status Register
(PCON)
The Power Control/Status Register, PCON has two sta-
tus bits that provide indication of which power-up type
reset occurred.
Bit0 is Brown-out Reset Status bit, BOR
. Bit BOR is set
on a Power-on Reset. It must then be set by the user
and checked on subsequent resets to see if bit BOR
cleared, indicating a BOR occurred. However, if the
brown-out circuitry is disabled, the BOR
bit is a "Don’t
Care" bit and is considered unknown upon a POR.
Bit1 is POR
(Power-on Reset Status bit). It is cleared on
a Power-on Reset and unaffected otherwise. The user
must set this bit following a Power-on Reset.
TABLE 12-3 TIME-OUT IN VARIOUS SITUATIONS
TABLE 12-4 STATUS BITS AND THEIR SIGNIFICANCE
TABLE 12-5 RESET CONDITION FOR SPECIAL REGISTERS
Oscillator Configuration
Power-up
Brown-out
Wake-up from
SLEEP
PWRTE
= 0 PWRTE = 1
XT, HS, LP 72 ms + 1024T
OSC 1024TOSC 72 ms + 1024TOSC 1024TOSC
RC 72 ms — 72 ms —
POR
BOR TO PD
0111Power-on Reset
0x0xIllegal, TO
is set on POR
0xx0Illegal, PD is set on POR
1011Brown-out Reset
1101WDT Reset
1100WDT Wake-up
11uuMCLR
Reset during normal operation
1110MCLR
Reset during SLEEP or interrupt wake-up from SLEEP
Condition
Program
Counter
STATUS
Register
PCON
Register
Power-on Reset 000h 0001 1xxx ---- --01
MCLR
Reset during normal operation 000h 000u uuuu ---- --uu
MCLR
Reset during SLEEP 000h 0001 0uuu ---- --uu
WDT Reset 000h 0000 1uuu ---- --uu
WDT Wake-up PC + 1 uuu0 0uuu ---- --uu
Brown-out Reset 000h 0001 1uuu ---- --u0
Interrupt wake-up from SLEEP PC + 1
(1)
uuu1 0uuu ---- --uu
Legend: u = unchanged, x = unknown, - = unimplemented bit read as '0'.
Note 1: When the wake-up is due to an interrupt and the GIE bit is set, the PC is loaded with the interrupt vector (0004h).
774.book Page 133 Tuesday, January 29, 2013 12:02 PM