National Instruments 653 Series User Manual page 90

Initial State
Reference
Point
Initial State ACK is deasserted.
1 The NI 653X sends an ACK pulse with programmable width to indicate that it
has data to generate, assuming the peripheral device has deasserted the REQ
signal. Otherwise, the ACK signal remains asserted until the peripheral device
deasserts the REQ signal.
2 The peripheral device can latch the data on the rising or falling edge of the ACK
pulse, or it can latch the data any time before asserting the REQ signal.
3 When the data is latched, the peripheral device must respond with an
active-going REQ signal edge.
When REQ
Asserted
Wait
For
REQ
Clear
ACK
Pulse
When REQ
Unasserted
© National Instruments Corporation
1
ACK
REQ
Figure 3-35. Long-Pulse Output Handshaking Sequence
Programmable
Delay
Wait
For
REQ
Figure 3-36. Long-Pulse Output State Machine
2
*
3
ACK and REQ are shown as active high.
Steps 1-3 are repeated for each transfer.
= Programmable Pulse Width
*
Action Steps
Initial State: ACK Cleared
Wait
For
Data
Send
ACK Pulse
Programmable
Delay
* With REQ-edge latching enabled, the data output is
delayed until the next inactive-going REQ edge.
3-35
Chapter 3
When 6533 Device has
data to output, output data.*
NI 653X User Manual
Timing Diagrams