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4. Functions
The sample data before and after the post-trigger (or, trigger only) are called pre-trigger sample and
post-trigger sample respectively.
Set the record length long to collect and observe longer waves like zoom out of the oscilloscope, and set
the record length short to collect and observe shorter waves like zoom in of the oscilloscope.
Usually the oscilloscope acquires the record data repeatedly. The record data finally acquired are
transferred in the form that plural record data continuously ranged as the figure shown below.
Duty ratio
The duty ratio shows the position of the post-trigger in a record.
The duty ratio also shows the ratio of record length for pre-trigger sampling and post-trigger sampling.
The duty ratio can be calculated as follows.
Duty ratio(%) = the number of pri-trigger samples / record length x 100
The position of the post-trigger moves to the left/right side in a record when the duty ratio is near to
0%/100%.
Memory and transfer mode
The block diagram about data transfer is shown below.
The data of channel 0 and channel 1 converted by each AD converter respectively are transferred to
device driver memory via the on-board memory.
The size of the on-board memory is 32M bytes (16M data), the size of device driver memory is
automatically secured by the driver and its maximum size becomes about 60M bytes.
The bus master transfer is performed from the on-board memory to device driver memory.
The maximum throughput (transfer ability) becomes 33MHz, 32 bits depending on the PCI bus
architecture.
On the other hand, the maximum transfer speed from the AD converter to the on-board memory
becomes 100MHz, 32 bits when the sampling of 100MHz is performed for 2 channels.
For that it exceeds the throughput of bus master transfer, the data cannot be transferred infinitely.
In this case, the acquisition operation is aborted by the overflow of the on-board memory.
When the digitizer is used in the oscilloscope mode, the latest acquisition data is transferred after
waiting for the on-board memory to ensure space.
Therefore, the loss should occur to the acquired waveform though the operation of the digitizer never
stops.
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DIG-100M1002-PCI
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