National Instruments 653X User Manual page 72

With REQ edge latching enabled (default), the REQ edge determines when data
Note
will be latched. Input data valid has to be held before the active going REQ edge a
minimum of t
next active going ACK signal edge is asserted.
Initial State
ACK
REQ
Reference
Point
Initial State ACK is deasserted.
1 When the 653X device has data to output, it drives the data onto the data lines,
and then asserts ACK. ACK stays asserted, indicating the 653X device is ready,
until the active-going REQ edge occurs.
2 The peripheral device responds with an active-going REQ signal edge. ACK
stays asserted, indicating the 653X device is ready, until the active-going REQ
occurs. Since the REQ is already asserted, the 653X device will wait until it
deasserts and reasserts to deassert the ACK signal and request additional data.
3 The asserted REQ signal deasserts the ACK signal.
4 To slow down the data transfer, you can insert a programmable delay before the
ACK signal is asserted.
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ns. With REQ edge disabled, input data valid has to be held t
rdi
1
2
Figure 3-17. Level ACK Output Handshaking Sequence
3
4
ACK and REQ are shown as active high.
Steps 1-4 are repeated for each transfer.
Action Steps
3-21
Chapter 3 Timing Diagrams
after the
adi
653X User Manual