Have problems of switch handshaking with DMM and other instruments

[AhGang]

Hi,

    In my systems, there are SMU PXI 4030, PXI Switch 2532, PXI DMM 4071.

    Both SMU and DMM will connect to DUT via PXI Switch. Handshaking between DMM and Switch is available yet handshaking between SMU and Switch is not.

    At the begging scan list including all connections (connections between SMU and DUT, connections between DMM and DUT) will be comminted into Switch.

   Problem is:

   The first 5 steps of scan list will advance with handshaking between Switch and DMM. The sixth step of scan list will be used for connecting SMU and DUT, so at

   this time, DMM can't shake hand with Switch and software trigger to Switch shall be used. But how can I perform this with best solution? I have 2 solutions:

  Solution 1:

          1) Configure sample count of niDMM Configure Multi Point as 5. DMM will stop sending trigger to Switch after measuring 5 samples (Is this configuration right? Do I need to configure trigger count?).

          2) Stop the Switch task (DAQmx Stop Task). Change the Switch advance trigger type from Digital Edge to Software.

          3) Use software trigger in the following steps of scan list.

 Solution 2:

          1) At the begging only 5 steps of scan list were committed into Switch.

          2) After DMM measurement ends, Stop the Switch task.

          3) Configure the following scan list with DAQmx Switch Creat Scan List

          4) Commit the scan list into Switch.

 Which solution makes sense?

 And another better solution?

Thanks

[PBear]

Hi AhGang,

With the SMU only supporting software triggering and the DMM supporting hardware triggering, you will have to do some clever programming to combine the two in a switching system. One way to do this, which doesn’t require reconfiguring your tasks, would be to set up a synchronous scan and take dummy readings with your DMM. These dummy readings would occur while the SMU is connected to your DUT and taking measurements. You would simply discard the readings of the DMM during this portion of your scan list. Configuring this way will have your switch always advance in the scan list upon receiving the measurement complete signal from the DMM. You will want to pay attention to the timing of the DMM measurement cycle to ensure that your SMU takes measurements while it is connected to each DUT. If this not an option, let me know and we can try some of your solutions.

[AhGang]

Hi Patrick,

     For the dummy reading of DMM, I need to reconfigure sample count and trigger count of DMM because the count of measurment data is different from the previous measurement. And before the SMU round of measuremnt, DMM shall be initiated first.

     Is that right?

[PBear]

Hi AhGang,

You don't need to reconfigure your DMM as it's readings don't matter when your SMU is sampling. The only thing you need to do is ensure that the SMU's measurements are complete before the DMM sends the measurement complete trigger. If you were taking 100 readings from the DMM before hand and your SMU is taking 12 readings, you don't need to set up your DMM to take 12 readings because you don't care about the readings anyway. You only care about the SMU readings and the time it takes to complete those should be less than what your DMM is taking to read.

Also, regarding your previous solutions, if you stop a scan list your scan list will default back to the beginning upon starting the task again. This rules out the first solution and defaults to the second. The other way would be to software time everything and send a software trigger once you’ve read in the data.

[AhGang]

I don't think so. Maybe I didn't describe the problem clearly.

There are some voltage settings change of SMU between DMM correct readings and dummy readings.

So DMM must stop measurement during SMU setting change. Otherwise, if DMM continue measurement during SMU setting change, switch will advance its scan list so that I can't assure SMU works on the sixth scan list. The way of stopping DMM measurement is to limit trigger count and sample count of correct readings and reconfigure trigger count and smaple count of dummy readings. The process flow is like this:

DMM measure 5 data (SMU is also working at this time)->DMM stops after getting 5 data, change SMU settings,reconfigure DMM,initiate DMM->DMM dummy readings and SMU working.

Thanks.

[PBear]

Hi AhGang,

If you need to reconfigure the SMU, I would probably recommend your second solution (reload a new scan list) and continue with software timing. Or do the entire thing with software timing. It sounds very much like you know the different options and what your application requirements are but I wanted to give you the idea of using the dummy measurements to advance the scan list. You may be able to adapt it to your application, I just wanted you to be aware of it. While our SMU is a great device, we do understand that using software timing may be a hindrance for some customers. A product suggestion has been filed on behalf of always beneficial customer feedback.

[AhGang]

Hi Patrick,

     Thanks for your suggestion.

     Can I creat 2 tasks with different scan lists at the initialization with DAQmx driver?

     task1: handshanking with DMM

     task2: software trigger with different scan list from the one in task1 

     And for the very first DMM measurment, I can use task1 with only 5 scan list steps.

     After that, stop task1 (do I need to clear task1) and start task2.

     Does this work?

     I would like to try but the instruments I ordered are on the way to me.

     Thanks.

     BR

[PBear]

Hi AhGang,

While you can set up two different tasks, only one task can be commited to the board at one time. This is important to note because while you can set up the tasks in your program in parallel and also start and stop them one after the other, the board can not store information about two tasks at the same time. When you call a start task, the driver then commits all the topology, trigger, scan list, etc. information to the board and then starts it. So yes, you can start a task after stopping another, but the information for the second task is sent to the board at the time you call the Start Task VI. The only draw back to this is that their is extra time to send the information and reprogram the board.

To get ready for your hardware, you can simulate devices in MAX and run test code. If you don't have the software yet, you can download our drivers (which come with MAX and many other software packages) at ni.com/downloads I believe you'll need NI-DAQmx, NI-SWITCH, NI-DMM, and NI-DCPOWER.