National Instruments 653X - Manual (Page 76)

Chapter 3 Timing Diagrams
© National Instruments Corporation 3-25 653X User Manual
Using the Trailing-Edge Protocol
Figure 3-20. Trailing Edge Input Handshaking Sequence
Figure 3-21. Trailing Edge Input State Machine
Reference
Point Action Steps
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.
ACK
REQ
2
1
ACK and REQ are shown as active high.
Steps 1-2 are repeated for each transfer.
3
Initial State
Data Latched
Wait
For
Space
Wait
For
REQ
Programmable
Delay
Programmable
Delay
Wait
For
REQ
When REQ
Unasserted
When 6533 Device
has space for data,
input data.*
Clear
ACK
When REQ
Asserted
Send
ACK
Initial State: ACK Cleared
* With REQ-edge latching enabled, the data input
is from the last inactive-going REQ edge.