CHAPTER 4 BUS CONTROL FUNCTION
User’s Manual U13850EJ4V0UM
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4.3.2 Bus width
CPU carries out peripheral I/O access and external memory access in 8-bit, 16-bit, or 32-bit. The following shows
the operation for each access.
(1) Byte access (8 bits)
Byte access is divided into two types, the access to even address and the access to odd address.
Figure 4-2. Byte Access (8 Bits)
0
7
0
7
8
15
Byte data
External data bus
(a) Access to even address
0
7
0
7
8
15
Byte data
External data bus
(b) Access to odd address
(2) Halfword access (16 bits)
In halfword access to external memory, data is dealt with as it is because the data bus is fixed to 16 bits.
Figure 4-3. Halfword Access (16 Bits)
0
0
15
15
Halfword data
External data bus
(3) Word access (32 bits)
In word access to external memory, lower halfword is accessed first and then the higher halfword is accessed.
Figure 4-4. Word Access (32 Bits)
0
15
0
15
16
31
Word data
External data bus
First
0
15
0
15
16
31
Word data
External data bus
Second