dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 70

• Manufacturer Part Number: dsp56800e
• Description: 16-bit Digital Signal Controller Core
• Manufacturer: Freescale Semiconductor, Inc

Data Types and Addressing Modes
Although a long-word value is always located on an even word address boundary, the effective address
used to access the value is not always that even word address. For all registers and addressing modes other
than the stack pointer (SP), the lower even address is used when accessing a long word. In an addressing
mode that uses the stack pointer, the effective address is the odd address that contains the upper word of
the 32-bit value. An attempt to access a long word in any other way generates a misaligned data access
exception. Refer to Section 9.3.3.2.3, “Misaligned Data Access Interrupt,” on page 9-9 for more
information.
Figure 3-11 shows a long-word access using an AGU pointer register. The example executes the
MOVE.L A10,X:(R0)
32-bit value contained in the A accumulator, $12345678, is written to this location and the following one.
Figure 3-12 shows a long-word access using the stack pointer. The example executes the
MOVE.L A10,X:(SP)
32-bit value contained in the A accumulator, $12345678, is written to addresses $1000 and $1001.
3-20
Figure 3-11. Accessing a Long Word Using an Address Register
Figure 3-12. Accessing a Long Word Using the SP Register
instruction, which uses the value in the R0 register, $1000, as a word address. The
instruction, which uses the value in the SP register, $1001, as a word address. The
Address
Address
Word
Word
DSP56800E Core Reference Manual
Instruction:
Access Size: Long
Effective Address: Even Value
Instruction:
Access Size: Long
Effective Address: Odd Value
$001000
$001000
SP
R0
MOVE.L A10,X:(R0)
MOVE.L A10,X:(SP)
15
15
1
5
1
5
X Memory
X Memory
$001000
$001001
2
6
2
6
3
7
3
7
4
8
4
8
0
0
Note: Even Effective Address
Note: Odd Effective Address
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