Fujitsu MB91460 SERIES FR60 User Manual page 565

Figure 4-13 Example of Connecting the MB91460 Series to External Devices
D31
to
D24
WR0
00
D31 D24 D23
4.2 Little Endian Bus Access
Little endian (LER) external bus access is performed for an area for which the little endian meth-
od is set.
Little endian bus access on the MB91460 series is implemented by using the bus access oper-
ation used for the big endian method. Basically, the order of output addresses and control signal
output are the same as for the big endian method and the byte locations on the data bus are
swapped in accordance with the bus width.
Note that, when a connection is made, the big endian area and the little endian area must be
kept physically separate.
■ Differences between Little Endian and Big Endian
The following explains the differences between little endian and big endian.
The order of addresses that are output is the same for little endian and big endian.
The data bus control signal used for 32/16/8-bit bus width is the same for little endian and big endian.
● Word access
The byte data on the MSB side for big endian address 00 becomes byte data on the LSB side when the little
endian method is used.
For a word address, the locations of all four bytes in the word are reversed:
00 -> 11, 01 -> 10, 10 -> 01, 11 -> 00
This LSI
D23 D15 D07
to to to
D16 D08 D00
WR1 WR2 WR3
01 10 11
D16 D15 D08 D07
32-bit device
(low-order 2 bits of
the address 00 to 11)
* For 16/8-bit devices, use the data bus on
the MSB side of this LSI.
0
D00 D15 D08 D07
*16-bit device
(low-order 1 bit of
the address 0/1)
Chapter 31 External Bus
4.Endian and Bus Access
1 0
D00 D07 D00
*8-bit device
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