PIC18F45J10 FAMILY
5.5
Configuration Mismatch (CM)
5.6
Power-up Timer (PWRT)
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.
PIC18F45J10 family devices incorporate an on-chip
Power-up Timer (PWRT) to help regulate the Power-on
Reset 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 PIC18F45J10
family devices is an 11-bit counter which uses the
INTRC source as the clock input. This yields an
approximate time interval of 2048 x 32 μs = 65.6 ms.
While the PWRT is counting, the device is held in
Reset.
In PIC18FXXJ Flash devices, the device Configuration
registers (located in the configuration memory space)
are continuously monitored during operation by
comparing their values to complimentary shadow reg-
isters. 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.
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 for details.
5.6.1
TIME-OUT SEQUENCE
A CM Reset behaves similarly to a Master Clear Reset,
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.
If enabled, 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 5-3, Figure 5-4,
Figure 5-5 and Figure 5-6 all depict time-out
sequences on power-up with the Power-up Timer
enabled.
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
(Figure 5-5). This is useful for testing purposes, or to
synchronize more than one PIC18F device operating in
parallel.
FIGURE 5-3:
TIME-OUT SEQUENCE ON POWER-UP (MCLR TIED TO VDD, VDD RISE < TPWRT)
VDD
MCLR
INTERNAL POR
TPWRT
PWRT TIME-OUT
INTERNAL RESET
DS39682E-page 44
© 2009 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
