Datasheet

PIC18F47J13 FAMILY
DS39974A-page 68 Preliminary  2010 Microchip Technology Inc.
5.5 Configuration Mismatch (CM)
The Configuration Mismatch (CM) Reset is designed to
detect, and attempt to recover from, random memory
corrupting events. These include Electrostatic
Discharge (ESD) events, which can cause widespread
single bit changes throughout the device and result in
catastrophic failure.
In PIC18FXXJ Flash devices, the device Configuration
registers (located in the configuration memory space)
are continuously monitored during operation by com-
paring their values to complimentary shadow registers.
If a mismatch is detected between the two sets of
registers, a CM Reset automatically occurs. These
events are captured by the CM
bit (RCON<5>). The
state of the bit is set to ‘0’ whenever a CM event occurs;
it does not change for any other Reset event.
A CM Reset behaves similarly to MCLR
, RESET
instruction, WDT time-out or Stack Event Resets. As
with all hard and power Reset events, the device
Configuration Words are reloaded from the Flash
Configuration Words in program memory as the device
restarts.
5.6 Power-up Timer (PWRT)
PIC18F47J13 family devices incorporate an on-chip
PWRT to help regulate the POR process. The PWRT is
always enabled. The main function is to ensure that the
device voltage is stable before code is executed.
The Power-up Timer (PWRT) of the PIC18F47J13 family
devices is a counter which uses the INTRC source as
the clock input. While the PWRT is counting, the device
is held in Reset.
The power-up time delay depends on the INTRC clock
and will vary from chip-to-chip due to temperature and
process variation. See DC parameter 33 (T
PWRT) for
details.
5.6.1 TIME-OUT SEQUENCE
The PWRT time-out is invoked after the POR pulse has
cleared. The total time-out will vary based on the status
of the PWRT. Figure 5-2, Figure 5-3, Figure 5-4 and
Figure 5-5 all depict time-out sequences on power-up
with the PWRT.
Since the time-outs occur from the POR pulse, if MCLR
is kept low long enough, the PWRT will expire. Bringing
MCLR
high will begin execution immediately if a clock
source is available (Figure 5-4). This is useful for
testing purposes or to synchronize more than one
PIC18F device operating in parallel.
FIGURE 5-2: TIME-OUT SEQUENCE ON POWER-UP (MCLR TIED TO VDD, VDD RISE < TPWRT)
TPWRT
VDD
MCLR
INTERNAL POR
PWRT TIME-OUT
INTERNAL RESET