National Instruments DIO 6533 - Manual (Page 69)

Chapter 5 Signal Timing
DIO 6533 User Manual 5-10 © National Instruments Corporation
Output
In output mode, the 6533 device raises the ACK signal after driving
output data to indicate new, valid output data. The peripheral device can
latch the data on the falling or rising edge of the ACK signal, or at any
time before returning a REQ pulse. The peripheral device must respond
with an active-going REQ signal edge to deassert the ACK signal and
request additional data.
To slow down the handshake, you can specify a data-settling delay to
occur before the ACK signal. This delay increases the setup time from
valid output data to the ACK signal.
Figure 5-8 shows an input transfer in level-ACK mode.
Figure 5-8. Level-ACK Mode Input
Wait
For
Space
Wait
For
REQ
Programmable
Delay
Programmable
Delay
Wait
For
REQ
When REQ
Asserted
Clear ACK
When 6533 Device
Has Space For Data,
Input Data*
When REQ
Unasserted
Initial State
ACK Cleared
Send
ACK
* With REQ-edge latching enabled, the data read
is from the last active-going REQ edge.