Advanced Features - PICO picoscope 3204 User Manual

3.4

Advanced features

3.4.1
Sampling modes
PicoScope 3000 Series PC Oscilloscopes can run in various sampling modes. At high
sampling rates, the oscilloscope collects 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 accurately timed data to be transferred back to the PC in
short blocks, without gaps.
3.4.2
More on block mode
In block mode, the computer prompts a PicoScope 3000 series PC Oscilloscope to collect
a block of data into its internal memory. When the 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 PC 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 PC 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(),
ps3000_stop()
3.4.3
More on streaming mode
In streaming mode, the computer prompts the PicoScope 3000 Series PC 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.
Copyright 2005 Pico Technology Limited. All rights reserved.
(not normally used) and
Technical reference
ps3000_get_values
ps3000_ready (),
().
ps3000_get_values ()
PS3000044 1.4
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