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CHAPTER 4 BUS INTERFACE
I External bus access
Figure 4.4-7 "External bus access in big-endian mode (16-bit Bus)" and Figure 4.4-8 "External
bus access in big-endian mode (8-bit Bus)" show external bus accesses under the following
conditions:
•
Data bus width: 16 bits and 8 bits
•
Data format: Word, halfword, and byte
These figures also show the access byte location, program address and output address, and
bus access count under each condition.
The MB91150 cannot detect misalignment errors.
Therefore, for word access, even if the lower two bits of the address specified by a program are
00, 01, 10, or 11, the lower two bits of the output address are always 00. For half word access,
00 is output if the two bits are 00 or 01, and 10 is output if the bits are 10 or 11.
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