Buffered Ad Bus System - Intel 80C186XL User Manual

BUS INTERFACE UNIT
ALE
A19:16
Latch
Address Bus
Processor
AD15:0
Address
Memory
Transceiver Data
Data Bus CS
or
I/O
DEN
Device
DT/ R
CPU Local Bus Buffered Bus
A1095-0A
Figure 3-31. Buffered AD Bus System
In a fully buffered system, DEN directly drives the transceiver output enable. A partially buffered
system requires that DEN be qualified with another signal to prevent the transceiver from going
active for local bus accesses. Figure 3-32 illustrates how to use chip-selects to qualify DEN.
DT/R always connects directly to the transceiver. However, an inverter may be required if the po-
larity of DT/R does not match the transceiver. DT/R goes low (0) only for memory and I/O read,
instruction prefetch and interrupt acknowledge bus cycles.
3-35