dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 207

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

6.5.4
Program memory accesses are always performed with word pointers. The general rules for word pointer
accesses, as discussed in Section 6.5, “Word Pointer Memory Accesses,” through Section 6.5.3,
“Accessing Data Structures,” apply to program memory accesses. However, many fewer addressing modes
are supported. The addressing modes that can be used when program memory is accessed appear in
Table 6-3.
6.6
Instructions that use address registers as byte pointers can only access bytes from data memory. An address
register value is interpreted as a byte pointer when an instruction with a “.BP” extension is used, such as
MOVE.BP or CLR.BP.
Table 6-4 on page 6-14 shows the byte address that is accessed for the different byte pointer addressing
modes. The address of the word that is accessed in memory is the byte address from the table, right shifted
1 bit; the LSB of the byte address in the table selects the upper or lower byte. Note that the X:xxxx and
X:xxxxxx addressing modes specify an absolute byte address, with the upper n – 1 bits specifying the
correct word in memory and the LSB selecting the upper or lower byte.
Freescale Semiconductor
Post-increment
P:(Rj)+
Post-update by offset N
P:(Rj)+N
Byte Pointer Memory Accesses
Accessing Program Memory
Addressing Mode
Bytes can not be accessed in the top half of data memory using byte
pointers. Bytes can still be accessed in the complete data memory space
using word pointers; but if byte pointers are used, only the lower half of
data memory can be accessed.
Table 6-3. Addressing Mode Arithmetic—Program Memory
Address Generation Unit
Address for Word Access
NOTE:
Rn+N
Rn+1
Byte Pointer Memory Accesses
Word accesses only
Word accesses only
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