National Instruments 653 Series User Manual page 70

Chapter 3 Timing Diagrams
Initial State: ACK Cleared
When REQ
Unasserted
Wait Wait
Programmable
For For
Delay
REQ Data
When 6533 Device has
data to output, output data.
Output Data,
Clear ACK
Then Send ACK
Wait
When REQ
For
Asserted
REQ
Figure 3-12. 8255-Emulation Output State Machine
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