Rev. 1.00, 09/03, page 102 of 704
6.5 Bus
Interface
The normal extended bus interface enables direct connection between the ROM and SRAM. For
details on the basic area and areas 1 to 3 bus specification selection, refer to tables 6.2 and 6.3.
For multiplex extended bus interface, only products compatible with this bus system can be
directly connected. For details on areas 1 to 3 bus specification selection, refer to tables 6.4 to 6.6
6.5.1
Data Size and Data Alignment
Data sizes for the CPU are byte, word, and longword. The BSC has a data alignment function, and
controls whether the upper data bus (D15 to D8/AD15 to AD8) or lower data bus (D7 to D0/AD7
to AD0) is used when the external address space is accessed, according to the bus specifications
for the area being accessed (8-bit access space or 16-bit access space) and the data size. The
multiplex extended address cycle is fixed to the bus specifications of the area being accessed (8-bit
access space or 16-bit access space).
8-Bit Access Space:
Figure 6.3 illustrates data alignment control for the 8-bit access space. With the 8-bit access space,
the upper data bus (D15 to D8/AD15 to AD8) is always used for accesses. The amount of data that
can be accessed at one time is one byte. A word access is performed as two byte accesses, and a
longword access, as four byte accesses.
D15/
D8/
D7/
D0/
Upper data bus
Lower data bus
Byte size
Word size
1st bus cycle
2nd bus cycle
Longword
size
1st bus cycle
2nd bus cycle
3rd bus cycle
4th bus cycle
AD15
AD8 AD7
AD0
Figure 6.3 Access Sizes and Data Alignment Control (8-Bit Access Space)
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