Using The Trailing-Edge Protocol - National Instruments 653X User Manual

Using the Trailing-Edge Protocol

Reference
Point
Initial State ACK is deasserted. The 653X device waits for the peripheral device to pulse
REQ to indicate it has data.
1 The 653X device sends an ACK pulse of programmable width when ready to
receive data.
2 After receiving the trailing edge of the ACK pulse, the peripheral device can
strobe data into the 653X device and pulse the REQ.
3 The 653X device sends another ACK pulse when ready for another input.
When REQ
Unasserted
Wait
For
REQ
When REQ
Asserted
Initial State: ACK Cleared
© National Instruments Corporation
ACK
Data Latched
REQ
Initial State
Steps 1-2 are repeated for each transfer.
Figure 3-20. Trailing Edge Input Handshaking Sequence
Programmable
Delay
Wait
For
REQ
Figure 3-21. Trailing Edge Input State Machine
1
2
ACK and REQ are shown as active high.
Action Steps
Space
Send
ACK
Programmable
Delay
Clear
ACK
* With REQ-edge latching enabled, the data input
is from the last inactive-going REQ edge.
3-25
Chapter 3
3
Wait
For
When 6533 Device
has space for data,
input data.*
Timing Diagrams
653X User Manual