Datasheet

© 2006 Microchip Technology Inc. DS70117F-page 47
dsPIC30F6011/6012/6013/6014
5.2 Reset Sequence
A Reset is not a true exception, because the interrupt
controller is not involved in the Reset process. The pro-
cessor initializes its registers in response to a Reset
which forces the PC to zero. The processor then begins
program execution at location 0x000000. A GOTO
instruction is stored in the first program memory loca-
tion immediately followed by the address target for the
GOTO instruction. The processor executes the GOTO to
the specified address and then begins operation at the
specified target (start) address.
5.2.1 RESET SOURCES
In addition to external Reset and Power-on Reset
(POR), there are 6 sources of error conditions which
‘trap’ to the Reset vector.
• Watchdog Time-out:
The watchdog has timed out, indicating that the
processor is no longer executing the correct flow
of code.
• Uninitialized W Register Trap:
An attempt to use an uninitialized W register as
an address pointer will cause a Reset.
• Illegal Instruction Trap:
Attempted execution of any unused opcodes will
result in an illegal instruction trap. Note that a
fetch of an illegal instruction does not result in an
illegal instruction trap if that instruction is flushed
prior to execution due to a flow change.
• Brown-out Reset (BOR):
A momentary dip in the power supply to the
device has been detected which may result in
malfunction.
• Trap Lockout:
Occurrence of multiple trap conditions
simultaneously will cause a Reset.
5.3 Traps
Traps can be considered as non-maskable interrupts
indicating a software or hardware error, which adhere
to a predefined priority, as shown in Table 5-1. They are
intended to provide the user a means to correct
erroneous operation during debug and when operating
within the application.
Note that many of these trap conditions can only be
detected when they occur. Consequently, the question-
able instruction is allowed to complete prior to trap
exception processing. If the user chooses to recover
from the error, the result of the erroneous action that
caused the trap may have to be corrected.
There are 8 fixed priority levels for traps: level 8 through
level 15, which implies that the IPL3 is always set
during processing of a trap.
If the user is not currently executing a trap, and he sets
the IPL<3:0> bits to a value of ‘0111’ (level 7), then all
interrupts are disabled but traps can still be processed.
5.3.1 TRAP SOURCES
The following traps are provided with increasing prior-
ity. However, since all traps can be nested, priority has
little effect.
Math Error Trap:
The math error trap executes under the following four
circumstances:
1. Should an attempt be made to divide by zero,
the divide operation will be aborted on a cycle
boundary and the trap taken.
2. If enabled, a math error trap will be taken when
an arithmetic operation on either accumulator A
or B causes an overflow from bit 31 and the
accumulator guard bits are not utilized.
3. If enabled, a math error trap will be taken when
an arithmetic operation on either accumulator A
or B causes a catastrophic overflow from bit 39
and all saturation is disabled.
4. If the shift amount specified in a shift instruction
is greater than the maximum allowed shift
amount, a trap will occur.
Address Error Trap:
This trap is initiated when any of the following
circumstances occurs:
1. A misaligned data word access is attempted.
2. A data fetch from and unimplemented data
memory location is attempted.
3. A data fetch from an unimplemented program
memory location is attempted.
4. An instruction fetch from vector space is
attempted.
Note: If the user does not intend to take correc-
tive action in the event of a trap error con-
dition, these vectors must be loaded with
the address of a default handler that sim-
ply contains the RESET instruction. If, on
the other hand, one of the vectors contain-
ing an invalid address is called, an
address error trap is generated.
Note: In the MAC class of instructions, wherein
the data space is split into X and Y data
space, unimplemented X space includes
all of Y space, and unimplemented Y
space includes all of X space.