Gage CompuScope 14100C, Hardware Manual And Driver Installation Manual

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26 CompuScope 85GC memory organization
A graphical representation of the above sequence is as follows:
Figure 18: Pre-Trigger: all data points in buffer valid
In the diagram above, the circular memory buffer is shown as an annulus with the physical memory address
ZERO at the top. Data storage is shown as a spiraling line going clockwise.
Storage starts at address ZERO and keeps on writing into the memory until it is filled (the spiraling line
completes a circle) and then starts overwriting the data stored in addresses ZERO, 1, 2...
Once a trigger event is detected, the address to which the data was being written into is tagged as the Trigger
Address, a specified number of Post-Trigger points are captured and then the acquisition is stopped.
The memory address at which the acquisition is stopped is designated as the End Address and the address after
that one is called Start Address.
Now, Pre-Trigger data lies between Start Address and Trigger Address, and Post-Trigger data between Trigger
Address and End Address.
It is clear from the diagram shown above that memory address ZERO is not necessarily the first point, or Start
Address, of the signal being captured. In fact, the physical address ZERO has very little significance in such a
system, as the trigger can happen at any time.