Motorola MC68030 User Manual page 282

The STOP instruction does not perform its function when it is traced. A STOP
instruction that begins execution with T1
=
1 and TO
=
0 forces a trace excep-
tion after it loads the status register. Upon return from the trace handler
routine, execution continues with the instruction following the STOP, and
the processor never enters the stopped condition.
8.1.8 Format Error Exception
Just as the processor checks that prefetched instructions are valid, the pro-
cessor (with the aid of a coprocessor, if needed) also performs some checks
of data values for control operations, including the coprocessor state frame
format word for a cpRESTORE instruction and the stack frame format for an
RTE instruction.
The RTE instruction checks the validity of the stack format code. For long
bus cycle fault format frames, the RTE instruction also compares the internal
version number of the processor to that contained in the frame at memory
location SP
+
54 (SP
+
$36). This check ensures that the processor can cor-
rectly interpret internal state information from the stack frame.
The cpRESTORE instruction passes the format word of the coprocessor state
frame to the coprocessor for validation. If the coprocessor does not recognize
the format value, it signals the MC68030 to take a format error exception.
Refer to SECTION 10 COPROCESSOR INTERFACE DESCRIPTION for details
of coprocessor-related exceptions.
If any of the checks previously described determine that the
for~at
of the
stacked data is improper, the instruction generates a format error exception.
This exception saves a short format stack frame, generates exception vector
number 14, and continues execution at the address in the format exception
vector. The stacked program counter value is the logical address of the in-
struction that detected the format error.
8.1.9
Int~rrupt
Exceptions
8-14
When a peripheral device requires the services of the MC68030 or is ready
to send information that the processor requires, it may signal the processor
to take an interrupt exception. Th.e interrupt exception transfers control to a
routine that responds appropriately.
MC68030 USER'S MANUAL
MOTOROLA