National Instruments 653X Manuale Utente

© National Instruments Corporation

Figure 3-23.  Trailing Edge Output Handshaking Sequence

Figure 3-24.  Trailing Edge Output State Machine

Initial State

ACK is deasserted.

1

The 653X device sends an ACK pulse of programmable width. This indicates 
new, valid output data.

2

The peripheral device responds with a REQ pulse. The trailing edge of the REQ 
pulse deasserts the ACK signal and requests additional data.

ACK

REQ

2

1

ACK and REQ are shown as active high.
Steps 1-2 are repeated for each transfer.

Initial State

Wait

For

Data

Wait

For

REQ

Programmable

Delay

Programmable

Delay

Wait

For

REQ

When REQ

Unasserted

When 6533 Device has 

data to output, output data.*

Clear

ACK

When REQ

Asserted

Initial State: ACK Cleared

Send
ACK 

* With REQ-edge latching enabled, the data output is

delayed until the next inactive-going REQ edge.