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CHAPTER 2 CPU
2.3.4
Multi-byte Data in Memory Space
Data is written to memory from the low-order address on. Therefore, for a 32-bit data
item, the low-order 16 bits are transferred before the high-order 16 bits.
If a reset signal is input immediately after the low-order bits are written, the high-order
bits might not be written.
■ Multi-byte data allocation in memory space
Figure 2.3-5"Sample allocation of multi-byte data in memory" is a diagram of multi-byte data configuration
in memory. The low-order eight bits of a data item are stored at address n, then next eight bits are stored at
address address n+1, etc.
Figure 2.3-5 Sample allocation of multi-byte data in memory
H
01010101
11001100
11111111
00010100
Address n
L
■ Accessing multi-byte data
Fundamentally, accesses are made within a bank. For an instruction accessing a multi-byte data item, address
FFFF
is followed by address 0000
H
an example of an instruction accessing multi-byte data.
80FFFF H
800000 H
62
of the same bank. Figure 2.3-6"Execution of MOVW A, 080FFFF
H
Figure 2.3-6 Execution of MOVW A, 080FFFFH
H
01 H
·
·
·
23 H
L
MB96300 Super Series Hardware Manual
MSB
01010101
11001100
AL before execution
AL after execution
LSB
11111111
00010100
??
??
01 H
23 H
" is
H
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