Chapter 3
Theory of Operation
© National Instruments Corporation
3-7
AT-DIO-32F User Manual
Leading Edge Mode
In leading edge mode, the handshaking lines REQ and ACK are viewed as pulses that are active
on the leading edge of the pulse. Once the data is read or written, TDELAY begins. After
TDELAY, ACK is sent to the digital I/O connector. When another leading edge of REQ is
received, DRDY is set and the AT-DIO-32F is ready for another cycle.
Figure 3-5 shows a read transfer in leading edge mode.
After TDELAY
Clear
ACK
pulse
DRDY
set
INIT
State
When REQ asserted
When REQ
unasserted
When REQ asserted
After data read
Start
TDELAY
LRESET
or
Power On
Send
ACK
Figure 3-5. Leading Edge Mode – Read
Note: If LPULSE is set, ACK starts when TDELAY starts.
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