Motorola MC68340 manual Lpstop, Move USP Movec Moves, Reset RTE Stop

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

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.

5.5.2.9PRIVILEGE 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.

5- 48MC68340 USER’S MANUALMOTOROLA

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