On the NI6711 AOs

[huygens]

With my NI card I have to control a laser scanning head, I need three AO
channes for the x,y and z axes and the fourth AO or a GP channel for PWM signal
that gives the laser output power. What I've done is to use the WFM functions
to load and to start my waveforms from a buffer. I had to create 4 different
buffers, one for each channel, and then to mix them toghether (multiplexing) to
be able to get out the 4 signals simultaneously. Otherwise I would have to send
4 couples of WFM_Load(Channel#) and WFM_Configure(Start) in sequence, but this
would cause a start lag time to each other. With this card I can't load the 4 AOs with
different buffers and letting them start at the same time, the AO_Configure(mode) works only for the
AO commands, no
t for WFMs. I'd also need to start the PWM signal before to output
the other 3 signals, and to change its DutyCycle and Frequency when
I decide to move the x,y,z axes and then to change them again when axes stop.
The CWPulse command that comes with Measurement Studio gives a flexible PWM out from
GPCTR_OUT1, but at the moment I had to put all the 4 waveforms (x,y,z and PWM) in the
same multiplexed buffer for sycro purpose.
Am I working properly with this card, or should I approach in a differnt way?
Thanks, Marco

[AlessioD]

Marco,
it seems like the key feature in your application will be the Duty cycle modulation. It is not that fast when you try to change the Duty Cycle of a DAQ-STC (67xx) counter on the fly. So probably the best thing is to have the PWM generated from a 4th AO, as you are already doing.
If the duty cycle swapping is not so important, then you might want to use the GPCTROut and synchronize it with the AO Update clock for the AO channels.
Regards,

AlessioD
National Instruments