National Instruments 653X Manuale Utente
Chapter 3
Timing Diagrams
© National Instruments Corporation
3-25
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.
REQ to indicate it has data.
1
The 653X device sends an ACK pulse of programmable width when ready to
receive data.
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.
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.
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,
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.