Intel 80C186XL, 80C188XL user manual Buffering the Data Bus, Clkout RD,WR DT/R DEN

BUS INTERFACE UNIT

3.6.1Buffering the Data Bus

The BIU generates two control signals, DEN and DT/R, to control bidirectional buffers or trans- ceivers. The timing relationship of DEN and DT/R is shown in Figure 3-30. The following con- ditions require transceivers:

•The capacitive load on the address/data bus gets too large.

•The current load on the address/data bus exceeds device specifications.

•Additional VOL and VOH drive is required.

•A memory or I/O device cannot float its outputs in time to prevent bus contention, even at reset.

T1 T2 T3 T4 T1

CLKOUT

RD,WR

DT/R

DEN

Write Cycle Operation

Read Cycle Operation

A1094-A0

Figure 3-30. DEN and DT/R Timing Relationships

The circuit shown in Figure 3-31 illustrates how to use transceivers to buffer the address/data bus. The connection between the processor and the transceiver is known as the local bus. A connection between the transceiver and other memory or I/O devices is known as the buffered bus. A fully buffered system has no devices attached to the local bus. A partially buffered system has devices on both the local and buffered buses.

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