National Instruments 653X User Manual page 78

Initial State
REQ
Reference
Point
Initial State ACK is deasserted.
1 The 653X device sends an ACK pulse of programmable width. This indicates
new, valid output data.
2 The peripheral device responds with a REQ pulse. The trailing edge of the REQ
pulse deasserts the ACK signal and requests additional data.
When REQ
Unasserted
Wait
For
REQ
When REQ
Asserted
© National Instruments Corporation
ACK
Figure 3-23. Trailing Edge Output Handshaking Sequence
Programmable
Delay
Wait
For
REQ
Figure 3-24. Trailing Edge Output State Machine
1
2
ACK and REQ are shown as active high.
Steps 1-2 are repeated for each transfer.
Action Steps
Initial State: ACK Cleared
Wait
For
Data
Send
ACK
Programmable
Delay
Clear
ACK
* With REQ-edge latching enabled, the data output is
delayed until the next inactive-going REQ edge.
3-27
Chapter 3
When 6533 Device has
data to output, output data.*
653X User Manual
Timing Diagrams