DSPIC30F2011AT-30ESLASHPF datasheet(49/228 Pages) MICROCHIP

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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:

Should an attempt be made to divide by zero,

the divide operation will be aborted on a cycle

boundary and the trap taken.

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.

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.

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:

A misaligned data word access is attempted.

A data fetch from and unimplemented data

memory location is attempted.

A data fetch from an unimplemented program

memory location is attempted.

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.

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