National Instruments 653X user manual *

Chapter 3 Timing Diagrams
653X User Manual 3-38 ni.com
Note With REQ edge latching enabled (default) REQ edge determines when data will be
latched. Input data valid has to be held before active going REQ edge a minimum of trdi ns.
With REQ edge disabled, it has to be held tadi after the next active going ACK signal edge
occurs.
Figure 3-35. Long Pulse Output Handshaking Sequence
Reference
Point Action Steps
Initial State ACK is deasserted.
1 The 653Xdevice sends an ACK pulse with programmable width to indicate that
it has data to output. 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 anytime before asserting the REQ signal.
3 Once 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