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Bit bus width – FUJITSU MB91460 SERIES FR60 User Manual

Page 562

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546

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"