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Chapter 31 External Bus
4.Endian and Bus Access
● 16-bit bus width
Figure 4-8 Relationship between Internal Register and External Bus Having 16-Bit Bus Width
● 8-bit bus width
Figure 4-9 Relationship between Internal Register and External Bus having 8-Bit bus Width
■ External Bus Access
Figure 4-11 "External bus Access for 16-Bit Bus Width" and Figure 4-12 "External Bus Access for 8-Bit Bus
Width" show external bus access (16-bit/8-bit bus width) separately for word, halfword, and byte access. The
following items are included in Figure 4-11 "External bus Access for 16-Bit Bus Width" and Figure 4-12 "External
Bus Access for 8-Bit Bus Width":
• Access byte location
• Program address and output address
• Bus access count
The MB91460 series does not detect misalignment errors.
Therefore, for word access, the lower two bits of the output address are always 00 regardless of whether 00, 01,
10, or 11 is specified as the lower two bits by the program. For halfword access, the lower two bits of the output
address are 00 if the lower two bits specified by the program are 00 or 01, and are 10 if 10 or 11.
read/write
D07
D15
D23
D31
D23
D31
"00"
External bus
Output address low-order digits
Internal register
"10"
AA
BB
CC
DD
AA
BB
CC
DD
D07
D15
D23
D31
D31
AA
BB
CC
DD
AA BB CC DD
read/write
"00"
External bus
Output address low-order digits
Internal register
"01"
"10"
"11"