pico Technology PicoScope 3425, User Manual

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Programmer's reference
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3.2.4
Sampling modes
PicoScope 3425 PC Oscilloscopes can run in various sampling modes.
Block mode. At the highest 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.
Streaming modes. At all but the highest sampling rates, these modes allow
accurately timed data to be transferred back to the PC without gaps. The
computer instructs the oscilloscope to start collecting data. The oscilloscope then
transfers data back to the PC without storing it in its own memory, so the size of
the data set is limited only by the size of the PC's memory. Sampling intervals
from less than one microsecond to 60 seconds are possible.
3.2.4.1
Block mode
In block mode, the computer prompts a PicoScope 3425 PC Oscilloscope to collect a
block of data into its internal memory. When the oscilloscope has collected the whole
block, it will signal that it is ready and then transfer the whole block to the computer's
memory through the USB port.
The maximum number of values depends upon the size of the oscilloscope's memory.
A PicoScope 3425 can sample at a number of different rates. These rates correspond
to the maximum sampling rate divided by 1, 2, 4, 8 and so on.
There is a separate memory buffer for each channel. When a channel is unused, its
memory can be borrowed by the enabled channels. This feature is handled
transparently by the driver.
The driver 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_ready() , ps3000_stop() and
ps3000_get_values() .
See Using block mode for programming details.
3.2.4.2
Using block mode
This is the general procedure for reading and displaying data in block mode:
1. Open the oscilloscope using ps3000_open_unit()
2. Select channel ranges and AC/DC coupling using ps3000_set_channel()
3. Using ps3000_set_trigger() , set the trigger if required
4. Using ps3000_get_timebase() , select timebases until the required number of
nanoseconds per sample is located
5. Start the oscilloscope running using ps3000_run_block()
6. Wait until the oscilloscope says it is ready using ps3000_ready()
7. Transfer the block of data from the oscilloscope using ps3000_get_values()
or ps3000_get_times_and_values()
8. Display the data
9. Repeat steps 5 to 8
10. Stop the oscilloscope using ps3000_stop()
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