Unwanted 5VDC (uS) Pulses on DAQCARD-1200 Digital Outputs
I'm currently using a DAQCard-1200 PCMCIA multifunction DAQ card to automate some "push-button" features on a particular piece of equipment. I've connected 3 of 8 Digital Outputs available on PortA in parallel with the momentary pushbutton switches used for manual control. To stimulate one of the switches, I am pulling the digital line low for 100mS then returning it to a high (the other signals should remain high during this time). I scoped the signals and noticed very short (uS) +5VDC-Pk pulses occuring on the idle lines (also on the digital lines I'm not even using). I'm using a the "Write to Port" VI. These "blips" occur during the rising "and" falling edges of the active signal. Occasionally, these
"blips" are long enough to trigger the other two inputs that I'd like to remain inactive. Besides using a filter to reduce the inverse-peak of the unwanted signals, is there a way to programatically control or remove these "blips" alltogether? Or are these even supposed to be there?
These blips can occur when writing to a digital port, and not masking the bits you do not wish to change.
If these blips are causing problems, take a look at the Write to Digital Port.VI. Double click on its icon to open its front panel. Go to its block diagram. You'll see where the port is configured on iteration 0, and then the Port Write is called, and there is an input to mask lines. This is what you'll need to do--put a value on this input to mask lines you want to remain the same. This should fix the blips you are seeing.
Also, if you are not manipulating more than one digital line at a time, you could use the Write to Digital Line.VI, which would accomplish the same thing. But if you need to update more than one line at the exact same ti
me, this method won't work for you.
Mark
Similar Messages
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USB-6009 pulse train generation with digital output....
Hello!
I've bought a new USB NI-Card (USB-6009) and now I'm trying to adopt an old vi that uses traditional DAQ drivers. I wrote that vi for a PCI NI-Card (PCI-6024E), which has two counters to generate two pulse trains simultaneously. Now I've only one counter and that's why I'm searching for a good way to create pulse trains using a digital output! The pulse trains are both ranging between 100 Hz and 100 kHz.
I'm sure somebody has an idea how I can solve the probem in the best way
Kind regards,
PeterYou can't do it with this low cost board. Both digital and analog outputs are software timed only. The analog out is rated at only 150 samples/sec and the digital is about the same. You can't even use one of the counters because it is not a hardware timed counter output. It is an event counter only as an input.
-
Create 4 digital output pulses base on input ttl signal
Hi
I am a beginner in Labview and would appreciate any advice on how to solve the following problem.
I am creating a TTL pulse train, and would like to send that into Labview as input. For every falling edge detected on the input signal, I'd like Labview to generate 4 digital output pulses. For each output pulse, I'd like to be able to specify the delay, and duration. The picture should illustrate it more clearly, with the numbers showing the intended order of magnitude.
System: NI PCI-6733 DAQ card, Labview 8.5
My daq card has 2 24-bit timers, and 8 digital I/O but I don't know what the best approach is for creating between 4-8 output pulses of this precision..should it be handled in hardware, or in software? And how would I go about it
Thanks,
-Sidney
NI Hardware: PXI-7853R, PCI-5122, PCI-6733, PXI-1036, PCI-MIO-16E-4, PCI-6110
Computer Hardware: Xeon Quad Core - 2.33 Ghz, 8 GB RAM
Software: Labview 2009, Labview FPGA 2009, Vista 64-bit, MAX 4.6, DAQmx 9.0, NI-SCOPE 3.5
Solved!
Go to Solution.Hi Yann,
Wow, thank you so much for this example! I'm trying to take a look at it, but when I run it.. it responds with the following error message
Error -200452 occurred at Property Node DAQmx Trigger (arg 1) in DAQmx Start Trigger (Digital Edge).vi:1->reprise-1.vi
Possible reason(s):
Measurements: Specified property is not supported by the device or is not applicable to the task.
Property: Start.TrigType
Task Name: _unnamedTask<49>
This is strange too, because ive already used the Digital Edge Start trigger for a different application with this card.
-Sidney
NI Hardware: PXI-7853R, PCI-5122, PCI-6733, PXI-1036, PCI-MIO-16E-4, PCI-6110
Computer Hardware: Xeon Quad Core - 2.33 Ghz, 8 GB RAM
Software: Labview 2009, Labview FPGA 2009, Vista 64-bit, MAX 4.6, DAQmx 9.0, NI-SCOPE 3.5 -
Pulse ON/OFF - digital outputs
I have this application where I need to turn ON a digital output for like 50ms or 100ms and turn it OFF. I call it Pulse COntrol
Here is an attachment jpg that shows how I am achieving it.
Another question if I may regarding loop timing. I have a while loop which iterates at 100ms. I choose a certain part of the program and make it a Subvi to clean the program to look more readable. Will the program still run at 100ms per iteration? For example, I have an equation that calculates a valuve from a analog input. To make the program clearer, I put the calculation into a subvi and send info and receive info through subvi panes. Will this affect the loop timing? I hope my question is clearer.
My program does a lot more than just calculate a value, hence wondering. THANKS!
vj
I may not be perfect, but I'm all I got!
Attachments:
p.JPG 22 KBhey VeeJay,
did you want suggestions for how to do your Pule Control a different way, or were you satisfied with the way you have it implemented in the code you sent a pdf of? thanks!
~kgarrett
Applications Engineer
National Instruments -
Trigger digital output at every 10 digital pulses
How can i generate an output pulse at every 10 input pulses comming from an encoder?
I need to trigger a sensor at every 10 encoder pulses to get data from the sensor.Hello jyp777,
What you will need is a counter with an if statement that activates a digital output every 10 ticks. To do this, I would look at a LabVIEW example titled: Counter - Count Edges (Continuous Clock) that can be found under Help >> Find Examples... >> Hardware Input and Output >> DAQmx >> Counter Input in LabVIEW. Using this example VI, it should be a simple step to add a condition that triggers a digital output when the count reaches 10.
You can also use a Digital Output example if you need help in this area. These examples can be found by going to :
Help >> Find Examples... >> Hardware Input and Output >> DAQmx >>Digital Output. I would recommend "Digital - Continuous Output.vi".
Happy LabVIEW coding!
Thanks,
Collin D.
Applications Engineer
National Instruments -
How can i deliver a single pulse of varying amplitude using Analog output and USB-6251?
I am trying to generate an analog output for the following waveform:
Pulse width: 300 usec, Frequency 40 Hz, Amplitude is following a sine wave with a 2 second period.
My approach is: Use an async timer with 1/[40 Hz] sec interval. I set the DAQ output rate at 1 MHz and the approach has been to generate and write 300 samples of the amplitude I need to send out, then wait for the next async interval callback , update amplitude etc etc. The assumption is that once the 300 samples are written and the task started , a 300 usec pulse would be sent out , task then stopped and then the analog output would be set to 0 waiting for he next pulse. The reality is that I get a stream of pulses of 300 usec which last the whole timer interval.
So , trying to establish whether what I am trying to do is feasible without actually sending a large array to the USB-6251 which would write zeros for the period after 300 usec.
Here is my timercallback code for review:
switch (event)
case EVENT_TIMER_TICK:
DAQmxErrChk(DAQmxStopTask(TaskAnalog));
Determine Voltage value algorithm here
//Generate Waveform and start Task
//Prepare AO arr
for (k=0;k<300;k++)
AOArr[k] = 0;
if (k<G_PulseWidth)
AOArr[k] = VOLTAGE_OUTPUT;
if (AOArr!=NULL)
DAQmxErrChk(DAQmxWriteAnalogF64 (TaskAnalog, (int32) 300 , 0, DAQmx_Val_WaitInfinitely, DAQmx_Val_GroupByChannel , AOArr, &sampsPerChanWritten, NULL));
DAQmxErrChk(DAQmxStartTask(TaskAnalog));
break;
ThanksI did resovle the issue I encountered. It was due to bad configuration of the Task.
My initial configuration was:
DAQmxErrChk(DAQmxCfgSampClkTiming(TaskAnalog, "",1.0E+06, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps , 300 * 1.0E+06));
which should be:
DAQmxErrChk(DAQmxCfgSampClkTiming(TaskAnalog, "",1.0E+06, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps , 300));
THis did it. works very well.
THanks -
Using a SCC counter pulse train to control a SCC digital out signal
I am trying to send a digital high signal on a SCC-Digital ouput module for a certain number of pulses generated by a SCC-Counter/timer pulse train. I have found examples of how to route such signals through PFI12 etc on an M-series board but I am trying to achieve this without referring to the card, just the SCC modules themselves.
I cannot find a way to use the sample clock from the counter generated pulse train to synchronise the digital output.
Is there any way I can do this without referring to the connected M-series DAQ card channels?
Thanks in advance for your assistance.
Cheers.Hi Phil,
The SCC carrier is only conditioning your signals (i.e. if your signals are not in optimal ranges, bandwidth or need external excitation). The actual counters and all digital lines are controlled directly by the M-series board. This means you will never be able to refer to a counter in the SCC module.
If you route the signals of the M-Series board, is as if you had done so externally from the SCC. Look at this example and might give you more insight to how to implement it (This is software timing). The hardware timing would be doing correlation DIO. Here is an example that needs to be modified to adapt to your timing: http://zone.ni.com/devzone/cda/epd/p/id/4414
Hope this helps,
Yardov
Gerardo O.
RF Systems Engineering
National Instruments
Attachments:
Finite Dig Output High.vi 31 KB -
Hi, to output a digital pulse on one of the digital output lines instead of the counter, do i just select the particular line instead of the counter for the device?
And if i'm only generating one pulse, and idle state is low, then does it matter what i choose as my low time?
Finally, using the Digital output DAQmx, when I write high to a line, will that line stay high until the remainder of the program (or until i write it low)?
Thanks.What type of DIO are you using? If using a standard DIO-96, you can use the Write to Digital Line function from the standard DIO functions. They are easier to use than DAQmx in this case. Just wire in the device number, channel number, line number, and True to output a high or False to output a low. Once a high is written to the line, it stays high until you write a low. The timing is up to you. You can write a high, wait some time, then write a low.
- tbob
Inventor of the WORM Global -
I am using a 6602 card with a counter in a simple pulse generation mode, and a rotary magnetic encoder.
I am trying to send a pulse after the certain position change. we have a standard encoder, and we are using the 6602 card with a programmed single pulse train generation counter. A channel of the encoder is set as a source, and after 50 pulses it is suposed to give a pulse. The problem is however when the encoder due to some noise factor sends pulses without a movement. This is not a problem with a position measurement, as it also has B channel to detect the change of the direction.
Is there a posibility to restart the delay counter, while reading the AqB signal, without a involvement of the software program?Hi Mirko,
I believe I understand your application now:
You want to count 50 pulses from your incremental encoder then generate a pulse output.
Right now it sounds like your are doing the following:
1. Using a counter on your NI 6602 to measure the angular position
2. When the position is reached that corresponds to 50 pulses then you turn a digital output high
3. Another counter on the NI 6602 is armed and waiting for a digital trigger, on receipt of the trigger it then generates a pulse.
It is not possible (that I know of) for a NI 6602 running a angular position task to generate a pulse output when a certain
position has been reached in hardware, this will need to be a software timed decision.
Why is the incremental encoder wired to the source of your counter?
I'm afraid this will always be a software timed event, the transition from measuring the position to generating a pulse (or pulse train).
This could be as fast as a millisecond if your VI was properly constructed.
If you need just a single pulse then why not use the software digital output to send a High then Low?
If you need a pulse train then look at the shipping examples that are included with Labview.
I'm attaching a quick example in Labview 8.2 that shows one concept that should work for you. This one count's edges then triggers a pulse train.
Have a great evening,
MatthewW
Applications Engineer
National Instruments
Attachments:
measureposition_counteroutput.vi 55 KB -
Finite pulse-train generation with variable time lapses with NiDAQmx
Being a newby in Labview and NiDAQmx, I find it tedious to program the application I need to drive my experiment : I want to generate a finite pulse train, with variable delays between two consecutive pulses. These delays are known before the experiment starts, summurized in a table (element 0 decribes the time lapse between pulse 0 and 1, element 1 between pulse 1 and 2 ...). I would like to use NiDAQmx to program this. I had in mind the following scheme : two counters, first one counting time between pulses, the second one generating the pulse once "counter one" has finished his job. What I don't figure out is how to reprogram "counter one"'s register, without introducing unwanted delays in the time
sequence of my finite pulse train. I am using a 6052E DAQ, and I want to generate delays in a same pulse train ranging from 1 microsecond up to 20 seconds.
Thank you for ANY help :-)Hello !
Well, I will try to be more precise while answering your questions. But first let me thank you very much for your help : your comments, questions and remarks are very helpful to help me shape my project, as you shed light on particular problems I strictly had no idea before !
1) I can certainly get on well with digital output as my flash device is triggered by TTL signals.
2) The lighting device is home-made, and I think it will be better for my needs to produce light throughout the duration of the input at the “on” level. In any case it will be driven by TTL-like signals. The intensity is manually set, so no analog control is required.
3) I will use Labview to collect the experimental data. The signal will be sampled during the light pulse : the rising edge of the TTL-like output signal will trigger both the lighting device and the data acquisition, the latter being stopped on the falling edge. The light emitted by the lighting device is called a “probe” for the following reasons : the photons are absorbed by the photosynthetic sample and “immediately” re-emitted at a longer wavelength. A photodiode acts as a signal transducer, and I monitor the intensity of this fluorescence. Knowing precisely when light pulses occurred after the initial start excitation (which is also a brief pulse of light but of a much greater intensity than the “probe” light) and the intensity of light emitted during theses pulses, I can reconstruct the kinetic of fluorescence decay. This kinetic reflects the behaviour of my biological sample. Thus no continuous acquisition is required as between two light pulses there is nothing to monitor. And all the half-time reaction are timed relative to the same “start” excitation as they reflect a jump sequence of an electron extracted by the “start” excitation : first jumps are quick ones (half-time in the 10 �s range) and last jumps are slow ones (half-time in the 1 s range). With respect to these kinetics, I would like a 1 �s precision. If not achievable, I could skip the quickest jump (but it would be a pity) and focus on the second one which has a 10 ms half-time reaction and a 100 �s precision would then be enough. But as we say in French : “Qui peut le plus, peut le moins !” (roughly meaning that when you can achieve the best, you easily can do the least). This precision relates to the position of one flash with respect to the others. I don’t need to be very precise on the duration of each individual light pulse : a typical value is 100 �s duration, but I can get on well with 90 �s or 110 �s, my data being an average of the light intensity emitted during the light pulse). All I want to know precisely is when it is fired.
4) Concerning the hardware, I already have a NI 6052E DAQ board, and unfortunately my laboratory cannot allow me to spend more money on this. I also have a fast acquisition board (IMTEC T3012) I intended to use to acquire my photodiode signal in place of the 6052E A/D converter. It has an old Labview driver, and I managed to upgrade it to suit my needs. It has an onboard segmented memory and can keep track precisely (it has a 60 MHz sample clock) of a trigger event. I am wondering if I can overcome the timing precision issue with this board, knowing that I strictly don’t care that flash n�1 is triggered at (t0 + 10 �s) or (t0 + 11 �s), provided that I know it, allowing me to place precisely my data point on the time scale. I can program the number of memory segments (i.e. the number of light pulses) and each one is filled with data coming from the photodiode upon receiving the rising edge triggering the light pulse. The precise date at which each triggered is received is stored in the board memory, allowing time reconstruction.
I do hope this is much clearer than my previous attempts ! Believe me, it is quite hard to leave biology for a while and enter the cryptic world of data acquisition !
Gritche -
How to measure the time a pulse is high for?
I am using Pulse measure.vi to measure the output of a comparator. My comparator output feeds to an LED. The duty cycle is 50% so the LED just flashes on and off. I want to measure the time the output is high ('ON time') and I have been getting this by just multiplying the pulse width measure by the no. of pulses but I want to modify it to measure the 'ON time' of random signals with different duty cycles...
The aim is that I am taking in a signal and need the LED to turn on when the signal 'ON time' reaches a certain specified time.
But before I continue with the LED I am wondering how to add up the time the signal is high for?Hi PinkLady4218,
You should be able to use one of the shipping examples to do what you need, please open LabVIEW and go to Help >> Find Examples.
From the Example Finder please go to Hardware Input and Output >> DAQmx >> Counter Measurements >> Period or Pulse Width >> Meas Buffered Semi-Period-Continuous.vi
You will then need to deinterleave the output array as it will show high time then low time then high time then ...
You will need to confirm the order these values appear and then you can use a function from the arrays palette and use the function "Decimate 1D Array"
Regards
JamesC
NIUK and Ireland
It only takes a second to rate an answer -
Hello!
My problem appeared when I tried to update my code from Traditional NI-DAQ Legacy to DAQmx.
I am using 2 counters (counter 5 and counter 7) from PCI-6602, to generate pulse train, and also the Digital I/O lines of the port 0 (the lines form 0 to 7). What I do in my application is that I am starting to generate the pulse train on the output of the 2 counters, and after that I am playing with the state of the digital lines.
In traditional there was no problem using the counters and the digital lines in the same time, everything was going perfectly, but in DAQmx this is not possible.
What happens: I start to generate pulse train on the output of the counters, no errors encountered, but when I try to modify the state of one line of the digital port the generation of the pulse train is stopped. This is happening when I start the task associated to the digital port.
My question is: it is possible to create a channel on the digital lines without altered the channels created for the counters?
Another thing what I manage to see using the "Measurement & Automation Explorer" and Test panels for PCI-6602, basically is the same thing, I generate pulse train on the output of the counter 7 and try to start a task on the digital line, but I get one error :
"Error -200022 occurred at Test Panel
Possible Reason(s):
Measurements: Resource requested by this task has already been reserved by a different task.
Device: Dev4
Terminal: PFI8"
Instead if I use the counter 0 or counter 1 to generate pulse train I don't encounter the same problem.
Which resources are used by the counters 2 to 7 from the PCI-6602 board and the counters 0 and 1 do not use?
Thank in advance for any replies!
Ciprian
Solved!
Go to Solution.Hello Jordan, thank you for your reply.
I am sorry but I can not see or run your example, I don't use LabView, I use Visual C++ for developing.
Here is the code for generating the pulse train:
GeneratePulseTrain(unsigned long ulCount1, unsigned long ulCount2)
short nStatus = 0;
nStatus = DAQmxCreateTask("",&m_taskHandle);
nStatus = DAQmxCreateCOPulseChanTicks (m_taskHandle, "Dev4/count5", "", NULL, DAQmx_Val_Low, 0.0, ulCount1,ulCount2);
if( bTriggerMode == true) // if hardware trigger is enabled
nStatus = DAQmxSetTrigAttribute (m_taskHandle, DAQmx_ArmStartTrig_Type, DAQmx_Val_DigEdge);
nStatus = DAQmxSetTrigAttribute (m_taskHandle, DAQmx_DigEdge_ArmStartTrig_Edge, DAQmx_Val_Rising);
nStatus = DAQmxSetTrigAttribute (m_taskHandle, DAQmx_DigEdge_ArmStartTrig_Src,"Dev4/PFI17" );
//set the internal timebase
nStatus = DAQmxSetCOCtrTimebaseSrc(m_taskHandle,"Dev4/count5","20MHzTimeBase" );
nStatus = DAQmxStartTask(m_taskHandle);
return nStatus;
And the code where I try to set the digital line:
SetChannelState(short nState)
short nStatus = 0;
uInt8 wrtBuf0[1]={0};
nStatus = DAQmxCreateTask("",&m_taskHandle);
// Configure line as output
nStatus = DAQmxCreateDOChan (m_taskHandle, "Dev4/port0/line0", "", DAQmx_Val_ChanPerLine);
nStatus = DAQmxStartTask(m_taskHandle);
wrtBuf0[0] = nState;
nStatus =DAQmxWriteDigitalLines (m_taskHandle, 1, 0, 0, DAQmx_Val_GroupByScanNumber , wrtBuf0, NULL, NULL);
nStatus = DAQmxWaitUntilTaskDone(m_taskHandle,10);
nStatus = DAQmxStopTask(m_taskHandle);
nStatus = DAQmxClearTask(m_taskHandle);
m_taskHandle = 0;
return nStatus; -
Hi,
I need to measure the cycle length of a pulse, calculate a delay based on this value, and then generate a triggered pulse with that delay value. The input and output pulses will be continuous. The best case would be to use the cycle length from one pulse in the calculated delay for the next pulse. One of my biggest problems has been getting the calculated delay value into the pulse specs.vi for the triggered output.
This output pulse will be used to trigger an IMAQ video acquisition; therefore, the solution to this problem will be part of a larger video acquisition application. This has posed a problem, in that accessing the counters has interfe
red with the triggered video acquisition.
Any suggestion will be welcome.
Thanks
DaveFilipe,
The overhead is the problem I'm trying to get around.
Specifically, what I need to do is to generate an output pulse after a trigger pulse, which is a given percentage of the cycle length. The input pulse is from heart rate, so it will have some variance, and the output pulse will be at a stationary point in the cardiac cycle. For example, for an input pulse of 2 Hz (500 ms) the user would likely request the output pulse be delayed by 75%. Therefore, the generated pulse will have a 375ms delay after the trigger.
In the past I have had hardware built to do this, but I am hoping I can accomplish the same thing with multiple counters on the 6602. I have been able to accomplish this with 3 counters (2 to measure period and 1 for output
) but the overhead prevents adequate triggering of the IMAQ video acquisition. I am hoping another method would solve this problem.
Thanks
Dave -
How to acquire analog signal and send a TTL pulse at the same time based on PXI 6123
Hi,
I am using a PXI-6123 data acquisition card, as the picture show in the attachment ,I want to acquire the analog signal of ai0 through reference analog window and at the same time send a TTL signal to trigger my camera. I have tried two methods, one is using the DAQmx Export signal.vi another is using DAQmx connect terminals, but when the data acquisition card acquire the analog signal, the DAQmx Export signal.vi and the DAQmx connect terminals sometime can send an TTL pulse ,sometime can not.
I don’t know why? or some other method that can achieve my arm is appreciated.
Regards
chunlei
Attachments:
method export signal.vi 21 KB
method connect terminal.vi 36 KB
Send a TTL pulse.JPG 288 KBHi,
Have things changed over the years?
I need to syncronise a digital output (Modul NI9474) and an analoge input (AI-Modul NI9203) module. I need to measure time intervals from a flank in signal A to a flank in signal B. I would like accuracies of the order of 1 ms. Currently, the signals are not synchronised, with errors of the order of 2 times the block length (block size x sample rate), sometimes much higher. The best I got so far was a block size of around 20 with a sample rate of 1 kHz.
If I use the master and slave settings on the RTSL settings, my program doesn't run properly.
If I use digital signals for input and output, I can syncronise them with RTSL settings and everything is good, but I can't always do that.
Also, if I do anything in the GUI (such as scrollowing something or going to another window), my output gets screwed up properly.
1. What can be done to synchronise AI with DO?
2. Is there something that can be done to avoid messing up the output when something happens in the user interface? (I know that I am messing up the outputs as they make some valves switch and that is loud).
Thanks in advance! -
At irregular occasions I need to grab counts from several counters, and buffering the counts must be done simultaneously for all counters. I'm modeling my approach after zone.ni.com/devzone/cda/tut/p/id/5404 which someone kindly pointed out in an earlier thread. However, that example only uses one counter, and you can't test the synchronization with only one counter, so I am using two counters configured the same way, and they're wired to a single benchtop signal generator (for example at 300 kHz).
What I want to do, I can test in a loop with a somewhat random wait in it. I want to drive a hardware digital output line high for a few ms and then low again. The hardware line is physically connected to terminals for my timing vi's Sample Clock Source and so will cause them to buffer their counts for later reading. After I pulse this line, when I know new good buffered counts await me, I want to read both my counters. If their bufferings are simultaneous, then each counter will have counted the same number of additional counts since the last loop iteration, which I can check by subtracting the last value sitting in a shift register and then subtracting the two "additional counts" values and displaying this difference as "Diff". It should always be 0, or occasionally +1 followed immediately by -1, or else the reverse, because buffering and a count could happen practically at the same moment.
When I do this using a flat sequence to control the relative timing of these steps, so the read happens after the pulse, the counters often time out and everything dies. The lengths of time before, during, and after the pulse, and the timeout value for the read vi, and the size of the buffer and various other things, don't seem to change this, even if I make things so long I could do the counting myself holding a clipboard as my buffer. I've attached AfterPulse.vi to illustrate this. If I get 3 or 10 or so iterations before it dies, I observe Diff = 0; at least that much is good.
When I use two flat sequences running in parallel inside my test loop, one to control the pulse timing, and the other to read the counters and do things with their results, it seems to work. In fact, Diff is always 0 or very occasionally the +/- 1 sequence. But in this case there is nothing controlling the relative timing such that the counters only get read after the pulse fires, though the results seem to show that this is true. I think the reads should be indeterminate with respect to the pulses, which would be unreliable. I don't know why it's working and can't expect it to work in other environments, can I? Moreover, if I set some of the pulse timing numbers to 1 or 2 or 5 ms, timeouts start happening again, too. So I think I have a workaround that I don't understand, shouldn't work, and shouldn't be trusted. See SeparateSequence.vi for this one.
I also tried other versions of the well-defined, single sequence vi, moving the counter reads to different sequence frames so that they occur with the Sample Clock Source's rising edge, or while it is high, or with the falling edge, and they also often time out. I'll post these if anyone likes but can't post now due to the attachment limit.
Here's an odd, unexpected observation: I have to sequence the reads of the counters to occur before I use the results I read, or else many of the cycles of this combine a new count from one counter with the one-back count from the other counter, and Diff takes on values like the number of counts in a loop. I though the dataflow principle would dictate that current values would get used, but apparently not so. Sequencing the calculations to happen after the reads fixes this. Any idea why?
So, why am I not succeeding in taking proper control of the sequence of these events?
Thanks!!!
Attachments:
AfterPulse.vi 51 KB
InSeparateSequence.vi 49 KBKevin, thanks for all the work.
>Have you run with the little execution highlighting lightbulb on? -Yes. In versions of this where there is no enforced timing between the counter and the digital line, and there's a delay inserted before the digital line, it works. There are nearly simultaneous starts on two tracks. Execution proceeds directly along the task wire to the counter. Meanwhile, the execution along the task wire to the digital high gets delayed. Then, when the digital high fires, the counter completes its task, and execution proceeds downstream from the counter. Note, I do have to set the timeout on the counter longer, because the vi runs so slowly when it's painting its progress along the wires. If there is any timing relationship enforced between the counter and the digital transition, it doesn't work. It appears to me that to read a counter, you have to ask it for a result, then drive the line high, and then receive the result, and execution inside the counter has to be ongoing during the rising line edge.
>from what I remember, there isn't much to it. There really aren't many candidate places for trouble. A pulse is generated with DIO, then a single sample is read from each counter. -Yup, you got it. This should be trivial.
>A timeout means either that the pulse isn't generated or that the counter tasks don't receive it. - Or it could mean that the counter task must be in the middle of executing when the rising edge of the pulse arrives. Certainly the highlighted execution indicates that. Making a broken vi run by cutting the error wires that sequence the counter read relative to the pulse also seems to support that.
>Have you verified that the digital pulse happens using a scope? -Verified in some versions by running another loop watching a digital input, and lighting an indicator, or recording how many times the line goes high, etc. Also, in your vi, with highlighting, if I delete the error wire from the last digital output to the first counter to allow parallel execution, I see the counter execution start before the rising edge, and complete when the line high vi executes. Also, if I use separate loops to drive the line high and to read the counter, it works (see TwoLoops.vi or see the screenshot of the block diagram attached below so you don't need a LV box). I could go sign out a scope, but think it's obvious the line is pulsing given that all these things work.
>Wait! I think that's it! If I recall correctly, you're generating the digital pulse on port0/line0... On a 6259, the lines of port 0 are only for correlated DIO and do not map to PFI. -But I'm not using internal connections, I actually physically wired P0L1 (pin 66) to PFI0 (pin 73). It was port0/line1, by the way. And when running some of these vi's, I also physically jumper this connection to port0/line2 as an analog input to watch it. And, again, the pulse does cause the counter to operate, so it clearly connects - it just doesn't operate the way I think it is described operating.
For what it's worth, there's another mystery. Some of the docs seem to say that the pulse has to be applied to the counter gate terminal, rather than to the line associated with the sample clock source on the timing vi. I have tried combinations of counter gate and or sample clock source and concluded it seems like the sample clock source is the terminal that matters, and it's what I'm using lately, but for example the document I cited, "Buffered Event Counting", from last September, says "It uses both the source and gate of a counter for its operation. The active edges on the gate of a counter is used to latch the current count register value in a hardware register which is then transferred via Direct Memory Access...". I may go a round of trying those combinations with the latest vi's we've discussed.
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