Motorola MC68030 User Manual page 52

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2-6
does not· require data to be aligned on word boundaries (refer to Figure
2-2), but the most efficient data transfers occur when data is aligned on the
same byte boundary as its operand size. However, instruction words must
be aligned on word boundaries.
The data types supported in memory by the MC68030 are bit and bit field
data; integer data of 8, 16, or 32 bits; 32-bit addresses; and BCD data (packed
and unpacked). These data types are organized in memory as shown in Figure
2-2. Note that all of these data types can be accessed at any byte address.
Coprocessors can implement any data types and lengths up to 255 bytes.
For example, the MC68881/MC68882 floating-point coprocessors support
memory accesses for quad-word-sized items (double-precision floating-point
values) .
. A bit operand is specified by a base address that selects one byte in memory
(the base byte) and a bit number that selects the one bit in this byte. The
most significant bit of the byte is bit 7.
31 23 15
LONG WORD $00000000
WORD $00000000
I
WORD $00000002
BYTE $00000000
I
BYTE $00000001 BYTE $00000002
I
BYTE $00000003
LONG WORD $00000004
WORD $00000004
WORD $00000006
BYTE $00000004
I
BYTE $00000005 BYTE $00000006
I
BYTE $00000007
•
•
' 7
•
•
' 7
L L
L
•
•
LONG WORD $FFFFFFFC
WORD $FFFFFFFC
I
WORD $FFFFFFFE
BYTE $FFFFFFFC
I
BYTE $FFFFFFFD BYTE $FFFFFFFE
I
BYTE $FFFFFFFF
Figure 2-1. Memory Operand Address
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