MC68340 datasheet(185/441 Pages) FREESCALE

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MC68340 USER’S MANUAL

MOTOROLA

All unimplemented instructions are reserved for use by Motorola for enhancements and

extensions to the basic M68000 architecture. Opcode pattern $4AFC is defined to be

illegal on all M68000 family members. Those customers requiring the use of an

unimplemented opcode for synthesis of "custom instructions," operating system calls, etc.,

should use this opcode.

Exception processing for illegal and unimplemented instructions is similar to that for traps.

The instruction is fetched and decoding is attempted. When the processor determines that

execution of an illegal instruction is being attempted, exception processing begins. No

registers are altered.

Exception processing follows the regular sequence. The vector number is generated to

refer to the illegal instruction vector or in the case of an unimplemented instruction, to the

corresponding emulation vector. The illegal instruction vector number, current PC, and a

copy of the SR are saved on the supervisor stack, with the saved value of the PC being

the address of the illegal or unimplemented instruction.

5.5.2.9 PRIVILEGE VIOLATIONS. To provide system security, certain instructions can be

executed only at the supervisor access level. An attempt to execute one of these

instructions at the user level will cause an exception. The privileged exceptions are as

follows:

• AND Immediate to SR

• EOR Immediate to SR

• LPSTOP

• MOVE from SR

• MOVE to SR

• MOVE USP

• MOVEC

• MOVES

• OR Immediate to SR

• RESET

• RTE

• STOP

Exception processing for privilege violations is nearly identical to that for illegal

instructions. The instruction is fetched and decoded. If the processor determines that a

privilege violation has occurred, exception processing begins before instruction execution.

Exception processing follows the regular sequence. The vector number (8) is generated to

reference the privilege violation vector. Privilege violation vector offset, current PC, and

SR are saved on the supervisor stack. The saved PC value is the address of the first word

of the instruction causing the privilege violation.

Freescale Semiconductor, Inc.

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