Address Space Types; Address Space Encodings - Motorola MC68030 User Manual

4.2 ADDRESS SPACE TYPES
The processor specifies a target address space for every bus cycle with the
function code signals according to the type of access required. In addition
to distinguishing between supervisor/user and program/data, the processor
can identify special processor cycles, such as the interrupt acknowledge cycle,
and the memory management unit can control accesses and translate ad-
dresses appropriately. Table 4-1 lists the types of accesses defined for the
MC68030and the corresponding values of function codes FCO-FC2.
Table 4-1. Address Space Encodings
FC2 FC1 FCO
Address Space
0
0 0 (Undefined, Reserved)*
0 0
1
User Data Space
0
1
0 User Program Space
0
1 1
(Undefined, Reserved)*
1
0 0 (Undefined, Reserved)*
1 0 1 Supervisor Data Space
1 1 0 Supervisor Program Space
1 1 1 CPU Space
*Address space 3 is reserved for user definition, while 0 and 4
are reserved for future use by Motorola.
The memory locations of user program and data accesses are not predefined.
Neither are the locations of supervisor data space. During reset, the first two
long words beginning at memory location zero in the supervisor program
space are used for processor initialization. No other memory locations are
explicitly defined by the MC68030.
A function code of $7 ([FC2: FCO] = 111) selects the CPU address space. This
is a special address space that does not contain instructions or operands but
is reserved for special processor functions. The processor uses accesses in
this space to communicate with external devices for special purposes. For
example, all M68000 processors use the CPU space for interrupt acknowledge
cycles. The MC68020 and MC68030 also generate CPU space accesses for
breakpoint acknowledge and coprocessor operations.
Supervisor programs can use the MOVES instruction to access all address
spaces, including the user spaces and the CPU address space. Although the
MOVES instruction can be used to generate CPU space cycles, this may
interfere with proper system operation. Thus, the use of MOVES to access
the CPU space should be done with caution.
MOTOROLA MC68030 USER'S MANUAL 4-5