161
7.4.3
Valid Strobes
Table 7-4 shows the data buses used and valid strobes for the access spaces.
In a read, the
RD
signal is valid without discrimination between 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 7-4
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
—
RD
Valid
Invalid
space
Write
—
HWR
Hi-Z
16-bit access
Byte
Read
Even
RD
Valid
Invalid
space
Odd
Invalid
Valid
Write
Even
HWR
Valid
Hi-Z
Odd
LWR
Hi-Z
Valid
Word
Read
—
RD
Valid
Valid
Write
—
HWR
,
LWR
Valid
Valid
Note:
Hi-Z: High impedance.
Invalid: Input state; input value is ignored.