Stepper/SGM fast scan axis

For stepping motors scans or spectra, motor pulses are used to provide the master clock pulse. This master clock pulse is also routed to the REQ input of the PCI-6534 (the board will be operated in pattern generation mode by a call to DIG_Grp_Mode() as described in Sec. 7.2).

For stepper scans, we will ``lock'' the XPZT and YPZT devices by asking the Delta Tau board to maintain a constant voltage output to the piezo amplifiers. The clock multiplexer will be instructed to use the appropriate motor pulse input as the master clock input, and the appropriate value of the clock divider will be set. The scan will then be generated line-by-line using instructions sent to the Newport MM-3000 units, possibly also with ZSTG positions streamed out from the NI PCI-6534 to the Delta Tau PMAC2 system.

For spectrum scans, we will calculate the correct ZSTG positions for all the wavelengths in the scan (the monochromator scans in wavelength, while ZSTG must be moved as the inverse of the wavelength). We will set the XPZT and YPZT values to a desired fixed value (or possibly stream one or the other to allow for $x/z$ and $y/z$ coupling corrections). We will then ask the monochromator to step through its wavelengths, and use the monochromator motor pulses as the master clock to cycle through the table of ZSTG (and possibly also XPZT and YPZT) positions.