Datasheet

Section 6 Bus Controller
Rev.7.00 Feb. 14, 2007 page 158 of 1108
REJ09B0089-0700
16-Bit Access Space: Figure 6.5 illustrates data alignment control for the 16-bit access space.
With the 16-bit access space, the upper data bus (D
15
to D
8
) and lower data bus (D
7
to D
0
) are used
for accesses. The amount of data that can be accessed at one time is one byte or one word, and a
longword transfer instruction is executed as two word transfer instructions.
In byte access, whether the upper or lower data bus is used is determined by whether the address is
even or odd. The upper data bus is used for an even address, and the lower data bus for an odd
address.
D
15
D
8
D
7
D
0
Upper data bus
Byte size
Word size
1st bus cycle
2nd bus cycle
Longword
size
• Even address
Byte size • Odd address
Lower data bus
Figure 6.5 Access Sizes and Data Alignment Control (16-Bit Access Space)