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CHAPTER 4 External Bus Interface
●
16-bit bus width
Figure 4.6-4 Relationship between internal register and external data bus of 16-bit bus width
●
8-bit bus width
Figure 4.6-5 Relationship between internal register and external data bus of 8-bit bus width
■ External Bus Access
External bus access (16-bit/8-bit bus width) is shown per word, half-word, and byte access in Figure 4.6-6
and Figure 4.6-7 . The following items are also shown in Figure 4.6-6 and Figure 4.6-7 .
• Access byte position
• Program address and output address
• Bus access count
The MB91191/MB91192 series do not detect the misalignment.
According to the word access, even if the address lower 2-bit specified by the program is "00", "01", "10",
or "11", the address lower 2-bit to be output will be all "00". In case of half-word access, when the lower
address is "00" or "01", "00" will be set, and when it is "10" or "11", "10" will be set.
D07
D15
D23
D31
D23
D3
1
"00"
External bus
Output addres lower
Internal register
"10"
AA
BB
CC
DD
AA
BB
CC
DD
read/write
External bus
Output addres lower
Internal register
D07
D15
D23
D31
"00"
D31
"01" "11""10"
AA
BB
CC
DD
AA BB CC DD
read/write
PA1/PA0
Output A1/A0
: Specified address lower 2-bit by program
: Output address lower 2-bit
: Output address start byte position
: Access data byte position
: Bus access count