Chapter 3
Timing Diagrams
©
National Instruments Corporation
3-35
Figure 3-35.
Long-Pulse Output Handshaking Sequence
Figure 3-36.
Long-Pulse Output State Machine
Reference
Point
Action Steps
Initial State
ACK is deasserted.
1
The NI 653
X
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.
ACK
REQ
1
3
2
ACK and REQ are shown as active high.
Steps 1-3 are repeated for each transfer.
*
= Programmable Pulse Width
*
Initial State
Wait
For
Data
Wait
For
REQ
Programmable
Delay
Programmable
Delay
Wait
For
REQ
When REQ
Asserted
When 6533 Device has
data to output, output data.*
Clear
ACK
Pulse
When REQ
Unasserted
Initial State: ACK Cleared
Send
ACK Pulse
* With REQ-edge latching enabled, the data output is
delayed until the next inactive-going REQ edge.
