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80C186EC/80C188EC Microprocessor User's Manual

80C186EC/80C188EC Microprocessor User's Manual

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BUS INTERFACE UNIT<br />

CLKOUT<br />

T1 TI TI<br />

ALE<br />

S2:0<br />

011<br />

AD15:0<br />

[AD7:0]<br />

Note 1<br />

Note 2<br />

Note 3<br />

[A15:8]<br />

Note 2<br />

Note 2 Note 3<br />

A19:16<br />

Note 4<br />

BHE<br />

[RFSH = 1]<br />

NOTES:<br />

1. The AD15:0 [AD7:0] bus can be floating, driving a previous write data value,<br />

or driving the next instruction prefetch address value. For an 8-bit device,<br />

A15:8 either drives the previous bus address value or the next instruction<br />

prefetch address value.<br />

2. The AD15:0 bus, or AD7:0 and A15:8 buses for an 8-bit device, drive to a<br />

zero (all low) at this time if Powerdown Mode is enabled. When Powerdown<br />

Mode is not enabled, the AD15:0 [AD7:0] bus either floats or drives previous<br />

write data, and A15:8 (8-bit device) continues to drive its previous value.<br />

3. The AD15:0 bus, or AD7:0 and A15:8 buses for an 8-bit device, drive to a<br />

zero (all low) at this time if Idle Mode is enabled. When Idle Mode is not<br />

enabled, the AD15:0 [AD7:0] bus either floats or drives previous write data,<br />

and A15:8 (8-bit device) continues to drive its previous value.<br />

4. The A19:16 bus either drives zero (all low) or 8H (all low except A19/S6,<br />

which can be high if the previous bus cycle was a DMA or refresh operation).<br />

If either Idle or Powerdown Mode is enabled, the A19:16 bus drives zeros<br />

(all low) at phase 1 of TI. Otherwise, the previous value remains active.<br />

Figure 3-25. HALT Bus Cycle<br />

A1088-0A<br />

3-31

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