How to write to one channel of a task with multiple channels? (plus other things...)

Question

So I have a USB-6009 DAQ.  It has 12 digital output lines.  I want one channel that is "Dev0\line0:10" which represents an address bus in my application.  And a second channel "Dev0\line11" which represents a program enable line in my application.
I have tried creating two different tasks and adding one channel to one task and the other channel to the other task.  The only task that worked was the task with "Dev0\line0:10".  It was always the task containing that channel, regardless of the order of creation.  So then I moved on to a different method.  (I read somewhere that I should only create one task of each type.  like only 1 DO task only 1 AO task etc...  However I am also using the two analog ouputs to and have a task for each AO and they work just fine.)
I tried add both channels to one task.  But when I needed to control only the address bus, I had to have some information for the other channel as well.  This was a little trying, but I could configure it that way.  But it turned out to be easier for me to just make one channel with all the lines and OR in the data for line11 with each write.
I just wondered if it was possible to write to one particular channel of a task and not the other channel?  That would really be the ideal solution for me.  especially if I could write multiple samples to the one channel while I left the other channel alone.  Which brings up another complaint... Why does WriteMultiSamplePort only work if I use a DigitalMultiChannelWriter, and not if I use a DigitalSingleChannel writer even though my task only has one channel (and by the way I set up the channel as one channel for all lines)?  A perplexing issue to be sure.
And no I can't just load all my samples into an array and write them all at once because I also have to manipulate the two analog outputs in between the various digital writes.
I am using NI DAQmx 7.5 and C#.  I am trying to use the DAQ to program a digital switch, which has proven to be a real challenge.  In push-pull mode there is too much ringing for the switches programming port to tolerate.  But the switches interface is LVTTL, so I needed the 3.3V.  When I changed to open-collector I had to use voltage dividers to drop down to 3.3V.  But the rise time using open-collector is too slow for me the program the switch in serial mode, so I had to change to parallel.  The switch has an 11 bit multi-plexed ADDR/DATA bus.  So the DAQ I had chosen to use which had plenty of lines for the serial programming, now is strained to it's absolute limits by the parrallel interface.   ARGH.  The only output I am not currently using is the counter, and I'm going to need it if I ever want to read back from the switch.  But first I have to seperate the ADDR/DATA bus from the CS line on the DIO lines of the DAQ.  And I don't know for sure what I'm going to do about the voltage level translation when I have to go bi-directional.  Maybe I can filter out the ringing in push-pull mode?  Any thoughts on that?

Answer 1

Hi Saikey,
In most cases, you are exactly right: you can only use one task for one type of operation (i.e. only one analog input task in the same program). With the USB 6009, you can have multiple digital output tasks running at the same time. I was able to run a digital output program with two different digital output tasks configured for a USB-6009.
However, you stated that it would be better if you had everything in a single task for your application and write data to only some of the channels. The easiest way to do this is to modify your array of output data so that only the data to that one channel is changing. So, for example, if you keep writing a 0 to the channels that do not need new data nothing will change.
If you have to change your analog outputs during this program, you could create an event structure that would stop and restart the analog output tasks without changing the digital output data. I hope that you find this information helpful.
Regards,
Hal L.