
CHAPTER 5 BUS CONTROL FUNCTION
User’s Manual U15905EJ2V1UD
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5.5.3
Access by bus size
The V850ES/SA2 and V850ES/SA3 access the internal peripheral I/O and external memory in 8-bit, 16-bit, or 32-
bit units. The bus size is as follows.
The bus size of the internal peripheral I/O is fixed to 16 bits.
The bus size of the external memory is selectable from 8 bits or 16 bits (by using the BSC register).
The operation when each of the above is accessed is described below. All data is accessed starting from the lower
side.
The V850ES/SA2 and V850ES/SA3 support only the little endian format.
Figure 5-2. Little Endian Address in Word
000BH
000AH
0009H
0008H
0007H
0006H
0005H
0004H
0003H
0002H
0001H
0000H
31
24 23
16 15
8 7
0
(1) Byte access (8 bits)
(a) 16-bit data bus width
<1> Access to even address (2n)
<2> Access to odd address (2n + 1)
7
0
7
0
Byte data
15
8
External data
bus
2n
Address
7
0
7
0
15
8
2n + 1
Address
Byte data
External data
bus
(b) 8-bit data bus width
<1> Access to even address (2n)
<2> Access to odd address (2n + 1)
7
0
7
0
2n
Address
Byte data
External data
bus
7
0
7
0
2n + 1
Address
Byte data
External data
bus