dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 208

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

Address Generation Unit
6.6.1
Both the MOVE.B and MOVE.BP instructions (and their unsigned counterparts) can be used to access
bytes in memory. The difference between them is how the address register operand is interpreted. When
the MOVE.B instruction is used, the address register operand is treated as a word pointer. When
MOVE.BP is used, the address register operand is treated as a byte pointer. Note that word pointers have
full visibility of the complete 32Mbyte data memory space, but when byte pointers are used, only the lower
half of data memory can be accessed.
Although it is possible to access bytes in memory with either type of pointer, there are times when using a
byte pointer makes more sense than using a word pointer, and at other times the opposite is true. Word
pointers can be used to access a data element of any size, so they should be used when mixed data is
6-14
No update
X:(RRR)
Post-increment
X:(RRR)+
Post-decrement
X:(RRR)–
Post-update by offset N
X:(RRR)+N
Indexed by offset N
X:(RRR+N)
Indexed by 3-bit offset
X:(RRR+x)
Indexed by 6-bit offset
X:(SP–xx)
Indexed by 3-bit offset
X:(SP–x)
Indexed by 16-bit offset
X:(RRR+xxxx)
Indexed by 24-bit offset
X:(RRR+xxxxxx)
6-bit absolute short
X:aa
6-bit peripheral short
X:pp
16-bit absolute address
X:xxxx
24-bit absolute address
X:xxxxxx
Addressing Mode
Byte Pointers vs. Word Pointers
Table 6-4. Addressing Mode Arithmetic—Byte Pointers to Data Memory
DSP56800E Core Reference Manual
Address for Byte Access
RRR+xxxxxx
RRR+xxxx
RRR+N
RRR+1
RRR–1
00xxxx
xxxxxx
RRR
—
—
—
—
—
—
Not allowed for SP register
Not allowed for SP register
Not allowed for SP register
Not allowed for SP register
Must use MOVE.B or MOVEU.B with word
pointer
Must use MOVE.B or MOVEU.B with word
pointer
Zero-extended 16-bit offset; not allowed for SP
register
Not allowed for SP register
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