Cronologic Ndigo5G-10, User Manual

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2.4.2 Zero Suppression
One of Ndigo5G’s key features is on-board zero suppression to reduce PCIe bus load. Only data
that passes specifications predefined by the user is transmitted. This guide refers to transmitted
waveform data as “packets”. A packet contains the waveform data and a timestamp giving the
absolute time (i.e. the time since start of data acquisition) of the packet’s last sample.
Figure 2.10 shows a simple example: Data is written to the PC only if values exceed a specified
threshold. Expanding on that, Ndigo5G’s zero suppression can be used to realize much more
complex scenarios.
timesta
mp
timesta
mp
Retrigger Precursor Postcursor
Figure 2.10: Simple zero suppression: Only data with values above a threshold are written to
the PC.
2.4.3 Trigger Blocks
Ndigo5G-10 and Ndigo5G-8 record analog waveforms using zero suppression. Whenever a rel-
evant waveform is detected, data is written to an internal FIFO memory. Each ADC channel
has one trigger block determining whether data is written to the FIFO. The parameters are set
in Structure
ndigo trigger block (See chapter 3.4.3 on page 34 ).
Each trigger block consists of two independent units that check the incoming raw data stream
for trigger conditions (Fig. 2.10 on page 10 ). Users can specify a threshold and can choose
whether triggering is used whenever incoming data is below or above the threshold (level trig-
gering) or only if data exceeds the threshold (edge triggering).
A gate length can be set to extend the trigger window by multiples of 3.2ns. Furthermore, if
users choose precursor values > 0, the trigger unit will start writing data to the FIFO precursor ·
3 . 2 ns before the trigger event.
When using edge triggering, all packets have the same length (Figure 2.11 on page 11 ):
cronologic GmbH & Co. KG 10 Ndigo5G User Guide