Refresh Bus Cycles; Write Bus Cycles; Read-Only Device Interface - Intel 80C186XL User Manual

BUS INTERFACE UNIT
3.5.1.1

Refresh Bus Cycles

A refresh bus cycle operates similarly to a normal read bus cycle except for the following:
•
For a 16-bit data bus, address bit A0 and BHE drive to a 1 (high) and the data value on the
bus is ignored.
•
For an 8-bit data bus, address bit A0 drives to a 1 (high) and RFSH is driven active (low).
The data value on the bus is ignored. RFSH has the same bus timing as BHE.
UCS
AD7:0
LA15:1
RD
AD15:8
3.5.2

Write Bus Cycles

Figure 3-21 illustrates a typical write bus cycle. The bus cycle starts with the transition of ALE
high and the generation of valid status bits S2:0. The bus cycle ends when WR transitions high
(inactive), although data remains valid for one additional clock. Table 3-4 lists the two types of
write bus cycles.
3-22
Note: A and BHE are not used.
0
Figure 3-20. Read-Only Device Interface
CE
O 0-7
27C256
A 0-14
OE
OE
A 0-14
27C256
O 0-7
CE
A1105-0A