AD4884BBCZ datasheet(82/116 Pages) AD

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Data Sheet

AD4884

DIGITAL FEATURES

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Rev. 0 | 82 of 116

Event Trigger Capture Mode, Read All FIFO

Event triggered mode can be used where ADC results immediately

prior to the event, as well as those after, are of interest to the user.

Once armed, the channel FIFO continuously fills with new ADC

results, storing up to, at most, 16,384 of the most recent results,

wrapping around and overwriting the oldest results in FIFO memory

once 16,384 captures are made.

Once a trigger event occurs, the FIFO continues to capture WA-

TERMARK number of results after the event. Only multiples of four

are valid values to set the FIFO_WATERMARK register when using

this mode. After an event has occurred, and the WATERMARK

number of results has been captured in the FIFO, no further new

results are captured until the FIFO is rearmed. The user must read

back all 16,384 FIFO results, and the value set for FIFO_WATER-

MARK allows the user to determine where in the FIFO result data

that the event occurred and also to distinguish between results

that occurred before the event and those which occurred after the

event, as shown in Figure 129 and Figure 130. In the full FIFO read

back, the first result after the event triggered is located at 16384 −

(FIFO_WATERMARK − 1), where FIFO_WATERMARK is the value

set prior to arming the capture. If this capture mode is armed and

an event occurs before the FIFO wraps around once, the FIFO

results before the event contain either results from previous FIFO

use or, when used for the first time after power cycling the device,

the FIFO contains random data in the FIFO data locations before

the event.

Figure 129. Event Capture Mode Read All FIFO Mode Example, FIFO Filling

Figure 130. FIFO Event Capture Mode Read All FIFO Mode Example, Locating

Event Position in FIFO

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