Rev. 1.0, 09/01, page 143 of 904
6.5.2
Valid Strobes
Table 6.3 shows the data buses used and valid strobes for the access spaces.
In a read, the
5'
signal is valid for both the upper and the lower half of the data bus. In a write,
the
+:5
signal is valid for the upper half of the data bus, and the
/:5
signal for the lower half.
Table 6.3
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)
8-bit access
Byte
Read
—
5'
Valid
Invalid
space
Write
—
+:5
Hi-Z
16-bit access
Byte
Read
Even
5'
Valid
Invalid
space
Odd
Invalid
Valid
Write
Even
+:5
Valid
Hi-Z
Odd
/:5
Hi-Z
Valid
Word
Read
—
5'
Valid
Valid
Write
—
+:5
,
/:5
Valid
Valid
Note:
Hi-Z: High-impedance state
Invalid: Input state; input value is ignored.
6.5.3
Basic Timing
8-Bit, 2-State Access Space: Figure 6.10 shows the bus timing for an 8-bit, 2-state access space.
When an 8-bit access space is accessed, the upper half (D15 to D8) of the data bus is used. The
/:5
pin is always fixed high. Wait states can be inserted.
Содержание H8S/2376 F-ZTAT
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