BEGIN
END
BEGIN
-
END
DATA STORAGE
Figure 9.4:
Ring buffer operation of memory
The physical memory therefore forms a ring buffer, into which information can
be continuously added (see Figure 9.4). This process of filling the ring buffer
memory terminates only when the recording logic indicates that the sweep must
be ended. Once the sweep recording has stopped, the content of the buffer
memory becomes available to the control PC for processing. This is also called
circular recording
. Sweep data is automatically moved from on
-
board RAM
memory to the recording file.
9.3.2
Pre
-
trigger sweeps
As we have seen, data emerging from the ADC is stored in the buffer memory.
When recording, the memory is continuously refreshed with new sample
values, until storage is halted. The information available in the memory is a
history
of the recorded signal up to the moment of “end
-
of
-
sweep”. The extent
of this history depends on the sample rate and the data storage capacity
(length) of the memory. If we assume a memory length of 40 000 samples and
a sample rate of 10 000 samples per second, then the time window of the
history will be:
(EQ 1)
twindow
=
=
40000
10000
4 seconds
Storage into the ring buffer can be stopped only by a “stop” signal from the
recorder. This signal is called the "trigger". For more information on triggering,
please refer to chapter “Digital Trigger Modes” on page 143.
GEN3i
I3763-3.1 en HBM: public
135
