BUS INTERFACE UNIT

AD15:8

8

A

 

 

 

 

 

 

 

DEN

 

OE

B

8

D15:8

MCS0

 

 

 

 

 

 

 

 

 

T

 

 

 

 

 

Buffer

 

 

Buffered

 

 

 

 

 

 

 

 

 

 

Data

 

 

 

 

 

Bus

AD7:0

8

A

 

 

 

 

 

 

 

 

 

OE

B

8

D7:0

 

 

 

DT/R

 

T

 

 

 

 

 

Buffer

 

 

 

 

 

 

8

 

Local

 

 

 

 

 

 

 

 

8

 

Data

 

 

 

 

Bus

 

 

 

 

 

 

 

 

 

 

A1058-0B

Figure 3-32. Qualifying DEN with Chip-Selects

3.6.2Synchronizing Software and Hardware Events

The execution sequence of a program and hardware events occurring within a system are often asynchronous to each other. In some systems there may be a requirement to suspend program ex- ecution until an event (or events) occurs, then continue program execution.

One way to synchronize software execution with hardware events requires the use of interrupts. Executing a HALT instruction suspends program execution until an unmasked interrupt occurs. However, there is a delay associated with servicing the interrupt before program execution can proceed. Using the WAIT instruction removes the delay associated with servicing interrupts.

3-36

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Image 117
Intel 80C186XL MCS0, Buffer Buffered Data Bus AD70, Buffer Local Data Bus, Synchronizing Software and Hardware Events