
Memory Interface
SC140 DSP Core Reference Manual 2-63
Figure 2-25 shows the memory accesses to the same memory area by both program fetches as well as data
accesses in big and little endian modes.
Figure 2-25. Instruction Moves in Big and Little Endian Modes
The Program Bus contents always appear as eight 16-bit little endian packed instructions, the memory
system performing a word (instruction) reversal in the case of big endian (program bus only).
0
8
16 ($10)
76543210
0
8
16 ($10)
01234567
Little EndianBig Endian
a0b0c0d0e0f0a1b1
c1d1e1f1a2b2
c2d2
e2f2
a3b3
c3d3e3f3
a1b1e0f0c0d0a0b0
c2d2a2b2e1f1
c1d1
e3f3
c3d3
a3b3e2f2
Memory
MOVE.4W from address $00
MOVE.L from address $08
64-bit XB-BUS
64-bit XA-BUS
InstructionsData Bus Contents Data Bus Contents
64-bit XB-BUS
64-bit XA-BUS
SC140 Core
128-bit P-BUS
c2d2_a2b2_e1f1_c1d1_a1b1_e0f0_c0d0_a0b0
Memory System Changes Big Endian to Little
a1b1_e0f0_c0d0_a0b0
xxxx_xxxx_e1f1_c1d1
Program Bus Contents (for both Endian cases)
FETCH (always 128 aligned) from address A0
MOVE.W from address $08
xxxx_xxxx_xxxx_c1d1
MOVE.B from address $08
xxxx_xxxx_xxxx_xxd1
a0b0_c0d0_e0f0_a1b2
xxxx_xxxx_c1d1_e1f1
xxxx_xxxx_xxxx_c1d1
xxxx_xxxx_xxxx_xxc1
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