HD64F2638F20J Datasheet, PDF (218/1512 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer H8S Family/H8S/2600 Series

Section 7 Bus Controller
H8S/2639, H8S/2638, H8S/2636,
H8S/2630, H8S/2635 Group
16-Bit Access Space: Figure 7-4 illustrates data alignment control for the 16-bit access space.
With the 16-bit access space, the upper data bus (D15 to D8) and lower data bus (D7 to D0) 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.
Byte size
Byte size
• Even address
• Odd address
Upper data bus
Lower data bus
D15
D8 D7
D0
Word size
Longword
size
1st bus cycle
2nd bus cycle
Figure 7-4 Access Sizes and Data Alignment Control (16-Bit Access Space)
Page 168 of 1458
REJ09B0103-0800 Rev. 8.00
May 28, 2010