Chapter 3
Timing Diagrams
3-20
ni.com
Figure 3-17.
Level-ACK Output Handshaking Sequence
Figure 3-18.
Level-ACK Output State Machine
Reference
Point
Action Steps
Initial State
ACK is deasserted.
1
When the NI 653
X
has data to output, it drives the data onto the data lines, and
then asserts ACK. ACK stays asserted, indicating the NI 653
X
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 NI 653
X
is ready, until the active-going REQ
occurs. Since the REQ is already asserted, the NI 653
X
waits until REQ 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.
ACK
REQ
1
2
3
4
ACK and REQ are shown as active high.
Steps 1-4 are repeated for each transfer.
Initial State
Wait
For
Data
Wait
For
REQ
Programmable
Delay
Programmable
Delay
Wait
For
REQ
When REQ
Asserted
Clear ACK
When 6533 Device has data
to output, output data.*
When REQ
Unasserted
Initial State: ACK Cleared
Send
ACK
* With REQ-edge latching enabled, the data output is
delayed until the next inactive-going REQ edge.
Summary of Contents for NI 653 Series
Page 1: ...PCI 6533...