Intel 80C188XL, 80C186XL user manual Device, Dt/ R, CPU Local Bus Buffered Bus

BUS INTERFACE UNIT

ALE
A19:16	Latch
Processor		Address Bus
AD15:0
				Address
	Transceiver	Data Bus	Data	Memory	CS
				or
DEN				I/O
				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.

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