Allocating Multiple-Byte Data In A Memory Space - Fujitsu F2MC-16LX Hardware Manual

CHAPTER 2 CPU
2.3

Allocating Multiple-byte Data in a Memory Space

In a memory space, the lower eight bits of multiple-byte data are stored at address n.
The remaining bits are stored at the addresses n + 1, n + 2, n + 3, ... in that order.
■ Allocating Multiple-byte Data in a Memory Space
As shown in Figure 2.3-1, data is written to memory in ascending order of addresses.
Therefore, if the data is 32 bit long, the lower 16 bits are first transferred and the higher 16 bits
are transferred subsequently.
If a reset signal is input immediately after the lower data is written, the higher data may not be
written. Therefore, to correctly retain the data, a reset signal must be input after the higher data
is written.
Figure 2.3-1 Example of Allocating Multiple-byte Data in a Memory Space
H
01010101
11001100
11111111
Address n
00010100
L
■ Access of Multiple-byte Data
As shown in Figure 2.3-2, all accesses are basically made within a bank. For an instruction that
accesses multiple-byte data, the next address after address FFFF
Figure 2.3-2 Example of Accessing Multiple-byte Data (Execution of MOVW A, 080FFFFH)
H
80FFFF
H
800000
H
L
30
MSB
01010101
AL before execution
01
H
23
H
11001100 11111111
H
??
AL after execution
23
H
LSB
00010100
is 0000 in the same bank.
H
??
01
H