Datasheet

© 2011-2012 Microchip Technology Inc. Preliminary DS39997C-page 69
PIC24FJ16MC101/102 AND PIC24FJ32MC101/102/104
6.9 Illegal Condition Device Reset
An illegal condition device Reset occurs due to the
following sources:
• Illegal Opcode Reset
• Uninitialized W Register Reset
• Security Reset
The Illegal Opcode or Uninitialized W Access Reset
Flag bit (IOPUWR) in the Reset Control register
(RCON<14>) is set to indicate the illegal condition
device Reset.
6.9.1 ILLEGAL OPCODE RESET
A device Reset is generated if the device attempts to
execute an illegal opcode value that is fetched from
program memory.
The illegal opcode Reset function can prevent the
device from executing program memory sections that
are used to store constant data. To take advantage of
the illegal opcode Reset, use only the lower 16 bits of
each program memory section to store the data values.
The upper 8 bits should be programmed with 0x3F,
which is an illegal opcode value.
6.9.2 UNINITIALIZED W REGISTER
RESET
Any attempts to use the uninitialized W register as an
address pointer will Reset the device. The W register
array (with the exception of W15) is cleared during all
Resets and is considered uninitialized until written to.
6.9.3 SECURITY RESET
If a Program Flow Change (PFC) or Vector Flow
Change (VFC) targets a restricted location in a pro-
tected segment (Boot and Secure Segment), that
operation will cause a security Reset.
The PFC occurs when the Program Counter is
reloaded as a result of a Call, Jump, Computed Jump,
Return, Return from Subroutine, or other form of
branch instruction.
The VFC occurs when the Program Counter is
reloaded with an Interrupt or Trap vector.
6.10 Using the RCON Status Bits
The user application can read the Reset Control regis-
ter (RCON) after any device Reset to determine the
cause of the Reset.
Table 6-3 provides a summary of Reset flag bit
operation.
TABLE 6-3: RESET FLAG BIT OPERATION
Note: The status bits in the RCON register
should be cleared after they are read so
that the next RCON register value after a
device Reset will be meaningful.
Flag Bit Set by: Cleared by:
TRAPR (RCON<15>) Trap conflict event POR, BOR
IOPWR (RCON<14>) Illegal opcode or uninitialized
W register access or Security Reset
POR, BOR
CM (RCON<9>) Configuration Mismatch POR, BOR
EXTR (RCON<7>) MCLR
Reset POR
SWR (RCON<6>) RESET instruction POR, BOR
WDTO (RCON<4>) WDT Time-out PWRSAV instruction,
CLRWDT instruction, POR, BOR
SLEEP (RCON<3>) PWRSAV #SLEEP instruction POR, BOR
IDLE (RCON<2>) PWRSAV #IDLE instruction POR, BOR
BOR (RCON<1>) POR, BOR —
POR (RCON<0>) POR —
Note: All Reset flag bits can be set or cleared by user software.