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3
Advanced features
3.1
Sampling modes
PicoScope 3000 series oscilloscopes run in various sampling modes. At high sampling rates, the
PicoScope 3000 series oscilloscope will collect data much faster than a PC can read it. To
compensate for this, the oscilloscope stores a block of data in an internal memory buffer, delaying
transfer to the PC until the required number of data points have been sampled. This is called block
mode. At very low sampling rates, you may want to switch to streaming mode. This allows data to
be transferred back to the PC as it is collected.
3.2
More on block mode
In block mode, the computer prompts an oscilloscope from the PicoScope 3000 series to
collect a block of data into its internal memory. When the PicoScope 3000 series
oscilloscope has collected the whole block, it will signal it is ready, and transfer the whole
block into computer memory via the USB port.
The maximum number of values depends upon the size of the oscilloscope's memory. A
PicoScope 3000 series oscilloscope can sample at a number of different rates. These
rates correspond to the maximum clock frequency multiplied by 0.5, 0.25, 0.125, and so
on.
There is a separate memory buffer for each channel. When a channel is unused, its
memory can be utilised by the enabled channels. On the faster models, one input can be
routed to two circuits in the oscilloscope, thus doubling the effective sampling rate of a
single channel.
The driver for a PicoScope 3000 series oscilloscope normally performs a number of setup
operations before collecting each block of data. This can take up to 50 milliseconds. If it is
necessary to collect data with the minimum time interval between blocks, avoid calling
setup functions between calls to ps3000_run_block(),
and
ps3000_get_values
3.3
More on streaming mode
In streaming mode, the computer prompts the PicoScope 3000 series oscilloscope to
start collecting data. The data is then transferred back to the PC without being stored in
oscilloscope memory. Data can be sampled with a period of between 1 ms and 60 s.
Data can be transferred by the oscilloscope's driver to a computer program either in
normal or windowed mode. In normal mode, any data collected since the last data
transfer operation is returned in its entirety. In windowed mode, a fixed number (n) of
samples is returned, where the oldest samples may have already been returned before.
Normal mode is useful if the computer program requires fresh data on every transfer.
Windowed mode is useful when the program requires a constant time frame of data.
Once the oscilloscope is collecting data in streaming mode, any setup changes (for
example, changing a channel range or AC/DC setting in the PicoScope software
application) will cause a restart of the data stream. The driver can buffer up to 32K
samples of data per channel, but the user must ensure that the
function is called frequently enough to avoid buffer overrun.
The
ps3000_get_times_and_values ()
mode.
Copyright 2005 Pico Technology Limited. All rights reserved.
().
function will always return FALSE (0) in streaming
Advanced features
ps3000_ready
(),
ps3000_stop()
ps3000_get_values ()
10
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