National Instruments 653X - Manual (Page 65)

Chapter 3 Timing Diagrams
653X User Manual 3-14 ni.com
Figure 3-10. 8255 Emulation Input State Machine
Wait
For
Space
Wait
For
REQ
Programmable
Delay
Wait
For
REQ
When REQ Unasserted,
Latch Input Data
When 6533 Device has
space for data, input data.
Clear
ACK
When REQ
Asserted
Initial State:
ACK Set
Send
ACK