BUS INTERFACE UNIT

T4

T1

T2

T3

T4

CLKOUT

 

 

 

 

ALE

 

 

 

 

S2:0

Valid

Status

 

 

AD15:0

Address

Data

 

RD / WR

 

 

 

 

A1507-0A

Figure 3-6. Typical Bus Cycle

 

TN

 

CLKOUT

Falling

Rising

Edge

Edge

 

 

Phase 1

Phase 2

 

(Low Phase)

(High Phase)

A1111-0A

Figure 3-7. T-State Relation to CLKOUT

Figure 3-8 shows the BIU state diagram. Typically a bus cycle consists of four consecutive T- states labeled T1, T2, T3 and T4. A TI (idle) state occurs when no bus cycle is pending. Multiple T3 states occur to generate wait states. The TW symbol represents a wait state.

The operation of a bus cycle can be separated into two phases:

Address/Status Phase

Data Phase

3-8

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Intel 80C186XL, 80C188XL user manual Clkout ALE, S20 Valid Status AD150 Address Data, Rd / Wr, Low Phase High Phase