Reference Classification - Motorola M68000 User Manual

supervisor mode. Therefore, when instruction execution resumes at the address specified
to process the exception, the processor is in the supervisor privilege mode.
The transition from supervisor to user mode can be
accomplished by any of four instructions: return from exception
(RTE) (MC68010 only), move to status register (MOVE to SR),
AND immediate to status register (ANDI to SR), and exclusive
OR immediate to status register (EORI to SR). The RTE
instruction in the MC68010 fetches the new status register and
program counter from the supervisor stack and loads each into
its respective register. Next, it begins the instruction fetch at
the new program counter address in the privilege mode
determined by the S bit of the new contents of the status
register.
The MOVE to SR, ANDI to SR, and EORI to SR instructions fetch all operands in the
supervisor mode, perform the appropriate update to the status register, and then fetch the
next instruction at the next sequential program counter address in the privilege mode
determined by the new S bit.

6.1.4 Reference Classification

When the processor makes a reference, it classifies the reference according to the
encoding of the three function code output lines. This classification allows external
translation of addresses, control of access, and differentiation of special processor states,
such as CPU space (used by interrupt acknowledge cycles). Table 6-1 lists the
classification of references.
MOTOROLA M68000 8-/16-/32-BIT MICROPROCESSORS USER'S MANUAL
Freescale Semiconductor, Inc.
NOTE
Table 6-1. Reference Classification
Function Code Output
FC2 FC1 FC0
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
*Address space 3 is reserved for user definition, while 0 and
4 are reserved for future use by Motorola.
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Address Space
(Undefined, Reserved)*
User Data
User Program
(Undefined, Reserved)*
(Undefined, Reserved)*
Supervisor Data
Supervisor Program
CPU Space
6- 3