Teledyne SP Devices ADQ7DC, Manual

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The memory is organized as a FIFO where it is possible to record data and read out data simultane-
ously. This is called readout-while-recording and is available both in multi-record and streaming mode.
If the readout process is as fast as the acquisition process, the memory size does not impose any lim-
itations.
If readout is scheduled after recording, the total data set from the measurement has to be limited to
4 GBytes to fit in the acquisition memory.
7.3 Acquisition modes
There are three main modes of data acquisition:
•
Continuous streaming, see Section 7.3.1 .
• Triggered streaming, see Section 7.3.2 .
• Multi-record, see Section 7.3.3 .
7.3.1 Continuous streaming acquisition
Continuous streaming means a constant flow of data from the ADQ to the host PC. At a trigger event or
start command (software trigger), the recording and data transfer starts,
Figure 30 . This continues until
stopped by the user.
Note that the data rate from the ADCs is up to 20 GBytes/s but the data rate to the PC is limited to
6.8 GBytes/s
1
. The continuous streaming mode thus assume some type of data reduction in the ADQ
to reduce the data rate to a level that the PC can handle. Some typical methods for data rate reduction
are listed below:
# DESCRIPTION USER COMMAND REF
a The channel mask selects which channels to record and which to
discard. SetStreamConfig
MultiRecordSetChannelMask
b The header generator apply header information to each record.
Select to turn headers on or off. SetStreamConfig
c The acquisition memory is a DRAM on the digitizer which operate
as a FIFO.
Figure 29: Acquisition memory.
ACQUISITION MODE RECORD SIZE –2A –4A –2C –4C –1X –2X
ACQUISITION MODE RECORD SIZE ADQ7DC 5 GSPS ADQ7DC 10 GSPS
Header < 256 samples > 5.9 % > 11 %
Header > 256 samples < 5.9 % < 11 %
Header Asymptotic lower limit 3.1 % 6.3 %
Raw mode no headers Any 0 % 0 %
Table 5: Header memory requirement for triggered streaming acquisition mode.
1. Theoretical limit. Dependent on host PC capacity and PCIe configuration.
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