I2CCON datasheet(67/210 Pages) MICROCHIP

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DS70139G-page 67

dsPIC30F2011/2012/3012/3013

8.2

Reset Sequence

A Reset is not a true exception because the interrupt

controller is not involved in the Reset process. The

processor 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

location 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.

8.2.1

RESET SOURCES

In addition to external Reset and Power-on Reset

(POR), there are six 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 causes a Reset.

• Illegal Instruction Trap:

Attempted execution of any unused opcodes

results 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 causes a Reset.

8.3

Traps

Traps can be considered as non-maskable interrupts

indicating a software or hardware error, which adhere

to a predefined priority as shown in Figure 8-1. 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

questionable 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 eight 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.

8.3.1

TRAP SOURCES

The following traps are provided with increasing

priority. However, since all traps can be nested, priority

has little effect.

Math Error Trap:

The math error trap executes under the following four

circumstances:

If an attempt is made to divide by zero, the

divide operation is aborted on a cycle boundary

and the trap is taken.

If enabled, a math error trap is 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 is 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 occurs.

Note:

If the user does not intend to take

corrective action in the event of a trap

error condition, these vectors must be

loaded with the address of a default

handler that contains the RESET instruc-

tion. If, on the other hand, one of the vec-

tors containing an invalid address is

called, an address error trap is generated.

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