MC68HC000RC12 Datasheet, PDF (88/189 Pages) Freescale Semiconductor, Inc – 8-/16-/32-Bit Microprocessors User’s Manual

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supervisor mode. Therefore, when instruction execution resumes at the address specified
to process the exception, the processor is in the supervisor privilege mode.
NOTE
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.
Table 6-1. Reference Classification
Function Code Output
FC2
FC1
FC0
Address Space
0
0
0
(Undefined, Reserved)*
0
0
1
User Data
0
1
0
User Program
0
1
1
(Undefined, Reserved)*
1
0
0
(Undefined, Reserved)*
1
0
1
Supervisor Data
1
1
0
Supervisor Program
1
1
1
CPU Space
*Address space 3 is reserved for user definition, while 0 and
4 are reserved for future use by Motorola.
MOTOROLA
M68000 8-/16-/32-BIT MICROPROCESSORS USER’S MANUAL
6-3
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