Section 6 Bus Controller
Rev. 3.00 Jan 25, 2006 page 124 of 872
REJ09B0286-0300
D15
D8 D7
D0
Upper data bus
Lower data bus
Byte size
Word size
1st bus cycle
2nd bus cycle
Longword
size
• Even address
Byte size
• Odd address
Figure 6.4 Access Sizes and Data Alignment Control (16-bit Access Space)
6.5.2
Valid Strobes
Table 6.9 shows the data buses used and valid strobes for each access space.
In a read, the
RD
signal is valid for both the upper and lower halves of the data bus. In a write, the
HWR
signal is valid for the upper half of the data bus, and the
LWR
signal for the lower half.
Table 6.9
Data Buses Used and Valid Strobes
Area
Access
Size
Read/
Write
Address
Valid
Strobe
Upper Data Bus
(D15 to D8)
Lower Data
Bus (D7 to D0)
Byte
Read
—
RD
Valid
Ports or others
8-bit access
space
Write
—
HWR
Ports or others
Byte
Read
Even
RD
Valid
Invalid
16-bit access
space
Odd
Invalid
Valid
Write
Even
HWR
Valid
Undefined
Odd
LWR
Undefined
Valid
Word
Read
—
RD
Valid
Valid
Write
—
HWR
,
LWR
Valid
Valid
Notes: Undefined
: Undefined data is output.
Invalid
: Input state with the input value ignored.
Ports or others
: Used as ports or I/O pins for on-chip peripheral modules, and are not
used as the data bus.
Содержание H8S/2158
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