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Дата изменения: Fri Feb 4 20:38:58 2005
Дата индексирования: Mon Oct 1 20:03:28 2012
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DSP board program

DSP board program forms all driving signals for DAC-ADC electronics and stepper motor controller. These driving signals set DAC values, start signal conversion, define stepper motor mode of operation, start and stop the motor. Driving signals formation is defined by scanning regime and by feedback parameters. There is a timer in DSP processor, that is allow to make presize synchronization of scanning process.

Measured signal value (it can be tunneling current, interaction force or other...) goes through ADC to signal processor, which evaluate feedback signal. For feedback signal evaluation standard scheme with integral and proportional gains is used. Afterwards values of measured signal and feedback signal go to a computer for further analysis.

The fact that feedback loop is closed on signal processor and computer doesn't participate in feedback signal evaluation allow to make feedback more stable and independent from computer work. What is important, it allow to control the microscope under systems like Windows 95 or NT. So, computer is processing data, and DSP board runs the tasks, in which time is critical.

Evaluated feedback signal goes to piezomanipulator's Z-axis. Beside this, program generate signals that move the probe in X- and Y- coordinates. Simultaneously with this movement image data can be obtained and stored in the buffer for further transmission to the computer (this is a scanning mode of operation), or movement can be done without data transfer (this is a positioning mode of operation). In the standard mode up to 2 ADC signals can be measured at the same time, and maximum amount of signals from ADC that can be measured simultaneously is 16. Also, by controlling stepper motor movements the program control movement of table with a sample. This regime is used to land or to retract a probe to the sample.

All feedback and movement parameters and ADC addresses can be set by changing variables that stored in signal processor memory, and it doesn't need to rebuild the program to do this. Thus scanning parameters can be tuned by changing these variables, so the microscope can be fully controlled by computer. This allow to automate scanning process. And by using network technologies fully supported by "FemtoScan" software, it is possible to drive the scanning process even from the other side of the Earth.