Rev. 1.00, 09/03, page 104 of 704
6.5.2 Valid
Strobes
Table 6.7 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 6.7
Data Buses Used and Valid Strobes
Area
Access
Size
Read/
Write
Address
Valid
Strobe
Upper Data Bus
(D15 to D8/AD15
to AD8)
Lower Data Bus
(D7 to D0/AD7 to
AD0)
8-bit access Byte
Read
—
RD
Valid
Ports or others
space Write
—
HWR
Ports or others
16-bit access Byte
Read
Even
RD
Valid
Invalid
space Odd
Invalid
Valid
Write
Even
HWR
Valid
Undefined
Odd
LWR
Undefined Valid
Word
Read
—
RD
Valid
Valid
Write
—
HWR
,
LWR
Valid
Valid
Note: Undefined:
Undefined data is output.
Invalid:
Input state with the input value ignored.
Ports or others:
Input/output pins for ports or on-chip peripheral devices cannot be used
as data buses.
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