Datasheet

PIC16C71X
DS30272A-page 54  1997 Microchip Technology Inc.
8.4.5 TIME-OUT SEQUENCE
On power-up the time-out sequence is as follows: First
PWRT time-out is invoked after the POR time delay has
expired. Then OST is activated. The total time-out will
vary based on oscillator configuration and the status of
the PWRT. For example, in RC mode with the PWRT
disabled, there will be no time-out at all. Figure 8-11,
Figure 8-12, and Figure 8-13 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 8-12). This is useful for testing purposes or to
synchronize more than one PIC16CXX device operat-
ing in parallel.
Table 8-10 and Table 8-11 show the reset conditions for
some special function registers, while Table 8-12 and
Table 8-13 show the reset conditions for all the
registers.
8.4.6 POWER CONTROL/STATUS REGISTER
(PCON)
The Power Control/Status Register, PCON has up to
two bits, depending upon the device.
Bit0 is Brown-out Reset Status bit, BOR
. Bit BOR is
unknown 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. The BOR bit
is a "Don’t Care" bit and is not necessarily predictable
if the Brown-out Reset circuitry is disabled (by clearing
bit BODEN in the Configuration Word).
Applicable Devices 710 71 711 715
Applicable Devices 710 71 711 715
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.
For the PIC16C715, bit2 is PER
(Parity Error Reset). It
is cleared on a Parity Error Reset and must be set by
user software. It will also be set on a Power-on Reset.
For the PIC16C715, bit7 is MPEEN (Memory Parity
Error Enable). This bit reflects the status of the MPEEN
bit in configuration word. It is unaffected by any reset of
interrupt.
8.4.7 PARITY ERROR RESET (PER)
The PIC16C715 has on-chip parity bits that can be
used to verify the contents of program memory. Parity
bits may be useful in applications in order to increase
overall reliability of a system.
There are two parity bits for each word of Program
Memory. The parity bits are computed on alternating
bits of the program word. One computation is per-
formed using even parity, the other using odd parity. As
a program executes, the parity is verified. The even par-
ity bit is XOR’d with the even bits in the program mem-
ory word. The odd parity bit is negated and XOR’d with
the odd bits in the program memory word. When an
error is detected, a reset is generated and the PER
flag
bit 2 in the PCON register is cleared (logic ‘0’). This indi-
cation can allow software to act on a failure. However,
there is no indication of the program memory location
of the failure in Program Memory. This flag can only be
set (logic ‘1’) by software.
The parity array is user selectable during programming.
Bit 7 of the configuration word located at address
2007h can be programmed (read as ‘0’) to disable par-
ity. If left unprogrammed (read as ‘1’), parity is enabled.
Applicable Devices 710 71 711 715
TABLE 8-5: TIME-OUT IN VARIOUS SITUATIONS, PIC16C71
TABLE 8-6: TIME-OUT IN VARIOUS SITUATIONS, PIC16C710/711/715
Oscillator Configuration Power-up Wake-up from SLEEP
PWRTE = 1 PWRTE = 0
XT, HS, LP 72 ms + 1024T
OSC 1024TOSC 1024 TOSC
RC 72 ms — —
Oscillator Configuration Power-up
Brown-out
Wake-up from SLEEP
PWR
TE = 0 PWRTE = 1
XT, HS, LP 72 ms + 1024T
OSC 1024TOSC 72 ms + 1024TOSC 1024TOSC
RC 72 ms — 72 ms —