dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 69

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

3.5.2
Word values are accessed from program or data memory with the MOVE.W or MOVEU.W instructions or
with any of the data ALU instructions that access an operand from data memory, such as
ADD.W X:(R0),A
Figure 3-9 shows an example of a word access using a word pointer. The example executes the
MOVE.W A1,X:(R0)
in X memory to which the value in A1 ($ABCD) is written.
3.5.3
Long-word values are accessed from data memory with the MOVE.L instruction or with any data ALU
instruction that accesses a long-word operand from data memory, such as
memory accesses always use a word address. Each long-word value occupies two memory word locations,
as shown in Figure 3-10, and is always aligned on an even word address except when SP is used. The even
address holds the lower word, and the odd address holds the upper word.
Freescale Semiconductor
Accessing Word Values Using Word Pointers
Accessing Long-Word Values Using Word Pointers
or
Address
Word
instruction. This instruction uses the value in the R0 register, $1000, as the address
DEC.W X:$C200
Figure 3-10. Correct Storage of 32-Bit Value in Memory
Figure 3-9. Accessing a Word with a Word Pointer
$001000
Address
Word
Data Types and Addressing Modes
Instruction:
Access Size: Word
Storage of $12345678 in Data Memory
15
$001000
1
5
. Word memory accesses always use an address as a word pointer.
X Memory
2
6
R0
15
3
7
MOVE.W A1,X:(R0)
A
X Memory
$001000
4
8
B
0
C
D
Odd Address: Always holds upper word
Even Address: Always holds lower word
0
ADD.L X:$1000,A
Memory Access and Pointers
. Long-word
3-19