Filter
Top Products
36
CHAPTER 2 CPU
2.6 Multi-byte Data in Memory Space
Data is written to memory from the low-order addresses. 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 inputted immediately after the low-order bits are written, the high-
order bits might not be written.
■ Multi-byte Data Allocation in Memory Space
Figure 2.6-1 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 address n+1, address n+2, address n+3, etc.
Figure 2.6-1 Sample Allocation of Multi-byte Data in Memory
■ Accessing Multi-byte Data
Fundamentally, accesses are made within a bank. For an instruction accessing a multi-byte data item,
address FFFF
H
is followed by address 0000
H
of the same bank. Figure 2.6-2 is an example of an instruction
accessing multi-byte data.
Figure 2.6-2 Execution of MOVW A, 080FFFF
H
H
L
01010101
11001100
11111111
00010100
MSB LSB
01010101
11001100 11111111 00010100
Address n
L
H
80FFFF
H
800000H
01H
23H
?? ??
23
H
01H
AL before execution
AL after execution
·
·
·