CHAPTER 4 BUS CONTROL FUNCTION
User’s Manual U12688EJ4V0UM00
110
(2) Halfword access (16 bits)
In halfword access to external memory, data is exchanged as is, or accessed in the order of lower byte, then
higher byte.
(a) When the data bus width is 16 bits
<1> Access to address 2n (even address)
<2> Access to address 2n + 1 (odd address)
7
0
Halfword
data
7
0
15
8
15
8
External
data bus
2n
2n + 1
Address
7
0
Halfword
data
7
0
15
8
15
8
External
data bus
2n + 1
Address
7
0
Halfword
data
7
0
15
8
15
8
External
data bus
2n + 2
Address
First
Second
Remark
n = 0, 1, 2, 3, ···
(b) When the data bus width is 8 bits
<1> Access to address 2n (even address)
<2> Access to address 2n + 1 (odd address)
7
0
Halfword
data
7
0
15
8
External
data bus
Address
7
0
Halfword
data
7
0
15
8
External
data bus
2n + 2
2n + 1
Address
First
Second
7
0
Halfword
data
7
0
15
8
External
data bus
Address
7
0
Halfword
data
7
0
15
8
External
data bus
2n + 1
2n
Address
First
Second
Remark
n = 0, 1, 2, 3, ···
(3) Word access (32 bits)
In word access to external memory, data is accessed in order from the lower halfword, then the higher
halfword, or in order from the lowest byte to the highest byte.
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