Configure VISA Read to terminate on unique character sequence

I am communicating with an instrument via a TCP connection using VISA read/write. The terminating character sequence from the instrument is "->" Is it possible to get VISA to terminate on this character sequence and basically not return these characters in a read?

No, it can only be configured to terminate on a single character. If you know that '>' will not appear in your data you can use that as your termination character. Otherwise you need to create your own read VI that will look for a sequence of characters as the termination value.
Mark Yedinak
"Does anyone know where the love of God goes when the waves turn the minutes to hours?"
Wreck of the Edmund Fitzgerald - Gordon Lightfoot

Similar Messages

Ways to configure VISA properties associated with the EOS character in LabVIEW

I am having a great deal of trouble reading consistently from an instrument (HP5328A Universal Counter) and am investigating the EOS character. In ibic, there are 6 properties of interest accessed through the ibconfig command. The following are the properties and their default settings:
Board level
- IbcEOSchar EOS character is 0 (zero)
- IbcEOSrd EOS is ignored during read operations
- IbcEOSwrt EOI not asserted when EOS sent
Device level
- IbcEOSchar EOS character is 0x0A (set in ibdev)
- IbcEOSrd EOS ignored during read operations
- IbcEOSwrt EOS not asserted when EOS sent
I would like to be able to programmatically set these at the beginning of my LabVIEW
program. The only relevant VISA properties in the INSTR or GPIB BoardInterface classes I can find are:
- Send End Enable
- Suppress End Enable
- Termination Character
- Termination Character Enable
The defaults in my LabVIEW program for both VISA classes mentioned are: Send End Enable is true; Suppress End Enable is false; Termination Character is \10 (Line Feed); and Termination Character Enable is false.
The only property I change is setting the Termination Character Enable to true for both classes. Is there anything else I can do with properties associated with the EOS char? Is there a property like the IbcEOSwrt that may have a part in generating a service request?
Just to confirm, the last two bytes of the instrument's ouput are \CR and \LF. I am using \LF as the EOS. Is this correct or should I be incorporating the \CR in the EOS somehow?
ANY input is appreciated,
Chris

Chris:
VISA "Termination Character" = NI-488 "IbcEOSchar"
VISA "Termination Character Enable" = NI-488 "IbcEOSrd"
VISA "Instr" or "GPIB Instr" = NI-488 "Device level"
VISA "GPIB BoardInterface" = NI-488 "Board level"
VISA cannot automatically add the termchar to the end of the written data (like IbcEOSwrt).
Unless you specifically need to do board-level communication, which is considered advanced, I suggest ignoring that, and sticking to the device-level calls.
If the instrument's ASCII data responses always end in \LF, then yes, just using \LF as the termchar is the correct thing. In fact, with most 488.2 devices you don't need to worry about the termchar, because the final byte of a response also contains EOI. EOI causes the driver to s
top reading from the instrument because it knows that is the end of the response.
You say you're having trouble, but you don't say what the symptom is. Is the read timing out? You might also want to use NI Spy to get a snapshot of what is going wrong.
I hope this helps some.
Dan Mondrik
Senior Software Engineer, NI-VISA
National Instruments

Error x3FFF0006 in VISA Read/Write

Hi,
I am getting this error message sometimes in VISA read and sometimes in VISA write. Its not consisten. Its only thrown in certain VIs. What could be the issue? I am attaching my main VI, where I configure serial port, and the VI where this error is thrown.
Thanks.
Attachments:
Main.vi ‏39 KB
Error.vi ‏30 KB

It's a warning and not an error.
The VI that is showing the warning is a little weird. You configure the serial port to terminate the read with a termination character but then when you do a read, specify the byte count and if the bytes read does not equal what you specify, you try to do another read. You usually don't do both.
If you specify a termination character with the VISA Configure Serial Port, the VISA Read will terminate when the termination character is detected. If you specify 100 bytes to read and there are only 50 bytes and a termination character, all you will read is 50 bytes. If you disable the termination character detection, you will always get the warning. In this case, as long as you use the VISA Bytes at Serial Port to verify that there really isn't any more data in the buffer, you can simply ignore the warning.

NI VISA read stops at zero character, returning an 0xBFFF003E error

Hi
I’m trying to read some serial data from a UUT using the NI-VISA read function. The data is mostly text but does include some control codes. The first of these appears after the ‘OK’ in the Serial Bytes window on the front panel. More text should follow but for some reason, the read function stops at the first zero character (index 144 in the Byte Array), and returns an 0xBFFF003E (-1073807298) error. I found another thread where someone had a similar problem and I’ve tried the fix for this plus a few other things, but nothing’s worked. If I use Hyperterminal, the entire data block is returned as it should be.
I wondered if this was anything to do with the 7.1 version of Labview I’m using (upgrade is on the cards). The version of NI VISA I’m running is 4.2.
Very much appreciate any thoughts.
Thanks
Bruce

The error code itself is a generic VISA error which often happens with USB to RS-232 interfaces. Does your device connect to the PC through USB as a virtual COMM port? If so what chip and Windows driver is it using?
Also your function somehow looks wrong. The only criteria for the read loop to terminate is if there is an error on the VISA read or the Teststand termination status gets true. Generally if you use VISA Bytes at Serial Port you are almost always doing something wrong! That function does absolutely not synchronize with anything in your data. You will read whatever is there at that moment and that could be a partial message, no bytes at all (LabVIEW is typically many times faster than any serial device even if it is super high speed), or multiple messages.
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

Why do I get a "termination character was read" warning with VISA read and TCPIP?

I am using VISA Reads with TCPIP raw sockets without issue with NI-VISA 3.0.1 but when I moved to NI-VISA 4.4 I was getting timeout errors. The timeout errors went away when I set the termination character enable property to true (which seemed to be default in NI-VISA 3.0.1), but now I get a warning stating that the "termination character was read".
Can I disable this warning? Can I set the termination character enable to default? How can I get rid of this annoying warning?
Solved!
Go to Solution.

Hey Dagwood,
Unfortunately there isn't a way to globally change the attribute VI_ATTR_TERMCHAR_EN to VI_TRUE. I spoke with R&D about possible use of the registries and they say it's not accessible through that. To address why this change was made, the developer who made the switch isn't around anymore so I can't find his reasoning as an explanation for you. The best this for you to do in your code would be while initializing, use the VISA Property Node to make the change and until that VISA Resource is closed, this change will remain set to the value you assign. I'm sorry we cannot provide any other solution for this inconvenience. Also, if you feel this is a large burden on your programming practice you can definitely submit a product suggestion for the ability to change global default values for VISA attributes.
Thanks,
David Pratt
AES - Test Side Products
NIC

VISA read timeout

I dont know why im getting a timeout error at the VISA read function(error says "timeout expired before operation completed"). I made sure the Labview serial port and my devices serial port are configured exactly the same. I even tested hyperterminal with the same port settings as in labview and it works perfectly but my labview program gives me an error. My device terminates each command it sends with a carriage return so i set up VISA READ to stop reading data when it encounters the CR character. I also made sure the carriage return was infact being sent by my device. Any thoughts?
Solved!
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I think it's not seeing your termination character on the read and/or write. When I send a string to the serial bus, I always use "Concatenate Strings" to add the appropriate termination character(s) to the end. Assuming your read termination is CR/LF, I've always had better luck stopping on the LF and stripping the CR with "Trim Whitespace."
Also, don't be afraid of making the timeout a second or two. If everything is going right, it will (normally) give the serial port plenty of time to complete its operation, but if things are going wrong, it will give you time to "notice" something is wrong.
Bill
(Mid-Level minion.)
My support system ensures that I don't look totally incompetent.
Proud to say that I've progressed beyond knowing just enough to be dangerous. I now know enough to know that I have no clue about anything at all.

Error -1073807253 occurred at VISA Read in transient SR830.vi VISA: (Hex 0xBFFF006B) A framing error occurred during transfer.

Hi,
I am have written a program with labview to make transient c-v measurement using a stanford research SR830 lockin amplifier. The program seems to be runing fine, but sometimes it is givvibg an error:
Error -1073807253 occurred at VISA Read in transient SR830.vi
Possible reason(s):
VISA: (Hex 0xBFFF006B) A framing error occurred during transfer.
Error -1073807253 occurred at VISA Read in transient SR830.vi
Possible reason(s):
VISA: (Hex 0xBFFF006B) A framing error occurred during transfer.
but if I press ok, the program again starts running. What might be the poblem? BTW I googled a bit and I see that in the labview topic "RS-232 Framing Error with HP 34401A Mulitmeter" by pkennedy32 this is what is said about framing error:
""Framing Error" in an RS-232 context means a very specific thing - when the receiver was expecting a stop bit, the line was not in SPACE condition. This can be the result of:
1... Baud rate mismatch (although other problems would likely crop up first).
2... Data Length problem, If I send 8 data bits and you expect 7, the stop bit is in the wrong place.
3... Parity setting mismatch - If I send 7 data bits + parity and you expect 7 data bits and no parity, the stop bit is in the wrong place.
4... Mismatch in # Stop bits - If I send you 7 Data bits + parity + one stop bit, and you expect 7 data bits + parity + TWO stop bits, the second one might not be correct, although most devices do not complain about this.
But, I must say that this is the same com port setting that I use to measure c-v hysterysis, but I never gt this error there.
I attach the program herewith for your kind perusal. Please help me resolve this issue.
Thanks in advance.
Solved!
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Attachments:
transient SR830.vi ‏94 KB
csac.vi ‏8 KB
sr830 initialize1.vi ‏15 KB

@Dennis Knutson you are right I checked the read indicator in backslash mode, and instead of a \n it is sending \r. So I changed the \n in my write strings to \r. But, if I keep the CLOSE VISA outside my loop instead of inside as you suggested, the termination character appears to come in the middle of the read string instead at the end. And since the read terminates at the \r so it is displaying some junk value before the \r, but if I put the CLOSE VISA outside the loop and play along with the bytes at the read buffer, I see the whole read string with the \r at the end of the string. But, whenever the values are in exponential form (when close to zero) like 6.938839 e-5, I always get a time out error whatever be the timeout that I put at the VISA initialize. And subsequently, if I stop the program and run it again the machine program hangs and I donot get any reading. Then after I close it again and start, sometimes it hangs for some more or starts working. If I put an arbitrarily large byte count at the READ VISA, then I always get the time out before the operation completed error.
@ Ravens Fan I have removed the CSAC VI altogether and taking the CH! And CH” reading separately, instead as one string. So, no more issues with that.
I use the control at the delay so that I can choose how much delay I want to set, and I use the math operation because I am using adding up the delay time to keep track of the time elapsed. Because in the end I have t plot a time vs. CH! And CH” readings.
I am not sure but probably I am making some silly errors. Please help me out.
Attachments:
transient SR830-2.vi ‏103 KB
sr830 initialize1.vi ‏15 KB

Can the carriage return within a variant be read as the termination condition for VISA READ?

Hi guys, I am trying to read a variant data using VISA READ. The VISA READ is set to terminate reading when it sees a carriage return.
Is there a chance that for the CR "encapsulated" within the variant be read by the VISA READ, and cause it to terminate?
Cheers!
Solved!
Go to Solution.

Since with the Flatten to String you are basically sending a binary representation of the data, you are going to have problems if you have the termination character enabled since byte 13 would be part of perfectly valid data and not just represent the end of a transmission.
What you might want to do is disable the termination character. Of course now you don't know how many bytes to read. So prepend your message to write with the number of bytes that are a part of the message (string length). You may want to use two bytes, (one byte would only give you messages up to 255 characters in length.)
Now on your reading end, read 2 bytes, convert them to a number and feed that number in the next VISA read which will then read that many bytes.
For examples, look at the TCP/IP read write examples in the example finder and you'll see how they send a message with 4 bytes to tell how much data makes up the rest of the message.

VISA Read timing issues

I am using an RS232 to control an older model Power Supply (OXFORD PS 120-10).
I have successfully written several VI's that all work, the only problem is that VISA Read takes WAY too long. I'm talking 10's of seconds to refresh. I need it have it refreshing in milliseconds or at least tens of seconds for the measurements we need. All of the VI's I have written have the same timing issue.
Attached is the most basic Serial Read/Write VI. Is there any way to improve the Read rate? Or might this just be an instrumentation issue. The strange thing is the Write commands work almost instantaneously (I can seem them on the instruments display).
Please help if you can, I've only been working with LabVIEW for a few weeks and am very must still in the learning process.
Thanks!
Solved!
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Attachments:
READandWRITE timing test.vi ‏14 KB
READandWRITE timing test.vi ‏14 KB

Do you have the communications protocol for the power supply? If you do not have everything right, you will have problems with communications.
Tens of seconds is a clue that you may be getting timeout errors because the default timeout is 10 seconds. Try placing an inidicator on the error out wire inside the loop (after Read) to see if an error occurs on any iteration. The way you have the VI set up you only see the error on the last iteration of the loop.
You are writing a carriage return to the instrument. If it requires that, it almost certainly sends a carriage return with the response. (This is why I asked about the protocol). If the instrument sends a carriage return (or other termination character), then you should Enable Termination Character on the Configuration VI and set the termination character to the correct value. The default is line feed (hex A or decimal 10). A carriage return is hex D or decimal 13. You must wire the numeric value to the termination character input for any value other than the default. Then change the byte count value (at the Read input) to a number larger than the longest message the instrument will ever send, perhaps 100 or 500. The Read will end as soon as the termination character is received, regardless of the number of characters.
I suspect that this is the problem - the instrument sends fewer than 10 characters in most messages but does send a termination character.
Lynn

VISA Read and Bytes at Port Timing Question

Hi,
I have a question that doesn't seem to be documented in the VISA Read function help. My application normally queries a serial instrument, waits, and then reads the port (with Bytes at Port property node wired to the byte count input of the VISA Read). However, I also need to be able to handle strings received from the instrument asynchronously without my vi requesting any data. So in the False Case in my vi (the True Case is where I write a command to the instrument) I have a Bytes at Port property wired to the VISA Read function's byte count input without using a VISA Write. This works fine if the \r\n terminated string is sent in one packet. However, sometimes there is a slight delay (only a few milliseconds) between characters. When that happens, the VISA Read returns, but I don't get the entire intended string. (Of course I know I have to keep reading in a loop until I get the \n and then assemble the received characters (sub strings) into my complete string for processing.)
This is my question: What is the time delay between characters at which the VISA Read terminates? This is not specified. I assume it could be as little as just slightly more than 1 stop bit at the baud rate being used. Does anyone know? NI employees?
When a string of more than one character (byte) is sent, as soon as the stop bit time has expired, the next start bit is normally sent immediately. Is it possible that if the next start bit doesn't come by, say, the mid-bit position time at the baud rate being used, the VISA Read returns immediately? Or does it wait at least 1 character time (at the baud rate)? This should be documented. Furthermore, for future versions it might be useful to add an input to the VISA Read to specify in milliseconds how long to wait AFTER the 'byte count' number of bytes have been received before returning the string (or character).
Thanks for your help.
Ed

I looked up the PC16550D data sheet (http://www.national.com/ds/PC/PC16550D.pdf). On p. 19 it says:
When RCVR FIFO and receiver interrupts are enabled, RCVR FIFO timeout interrupts will occur as follows:
A. A FIFO timeout interrupt will occur, if the following conditions exist:
    - at least one character is in the FIFO
    - the most recent serial character received was longer than 4 continuous character times ago (if 2 stop bits are programmed the second one is included in this time delay).
    - the most recent CPU read of the FIFO was longer than 4 continuous character times ago.
The maximum time between a received character and a timeout interrupt will be 160 ms at 300 baud with a 12-bit receive character (i.e., 1 Start, 8 Data, 1 Parity and 2 Stop Bits).
B. Character times are calculated by using the RCLK input for a clock signal (this makes the delay proportional to the baudrate).
C. When a timeout interrupt has occurred it is cleared and the timer reset when the CPU reads one character from the RCVR FIFO.
D. When a timeout interrupt has not occurred the timeout timer is reset after a new character is received or after the CPU reads the RCVR FIFO.
So, this UART uses 4 character times to determine that no more characters are coming in. And the delay is baud-rate dependent. This makes sense because I see that at, say, 115200 baud I receive more "partial strings" than I do at 9600 baud (where the sending device has more time to send the next character)!
Kudos for making me investigate this further! Thanks for listening. Hope this may help others in the future.

The vi is identifyng the number of bytes to be read but the VISA Read vi is not able to read the data from the port.

We are trying to communicate with the AT106 balance of Mettler Toledo.The VI is attached.
We are sending in "SI" which is a standard command that is recoginsed by the balance. The balance reads it.The indicator after the property node indicates that there are 8 bytes available on the serial port. However, the VISA read VI fails to read the bytes at the serial port and gives the following error:
Error -1073807253 occurred at VISA Read in visa test.vi
Possible reason(s):
VISA: (Hex 0xBFFF006B) A framing error occurred during transfer.
The Vi is atttached.
Thanks
Vivek
Attachments:
visa_test.vi ‏50 KB

Hello,
You should also definitely check the baud rates specified; a framing error often occurs when different baud rates are specified, as the UARTs will be attempting to transmit and receive at different rates, causing the receiving end to either miss bits in a given frame, or sample bits more than once (depending on whether the receiving rate is lower or higher respectively). You should be able to check the baud rate used by your balance in the user manual, and match it in your VI with the baud rate parameter of the VISA Configure Serial Port VI.
Best Regards,
JLS
Best,
JLS
Sixclear

VISA Read gets incorrect data from serial connection

I am having difficulty using the VISA functions in LabVIEW to read data from a virtual COM port. Data is being sent from a serial to USB chip via a USB connection using OpenSDA drivers. I have a python program written to read from this chip as well, and it never has an issue. However, when trying to achieve the same read in LabVIEW I am running into the problem of getting incorrect data in the read buffer using the VISA Read function.
I have a VISA Configure Serial Port function set up with a control to select the COM port that the device is plugged into. Baud rate is default at 9600. Termination char of my data is a newline, which is also default. Enable termination char is set to true. A VISA Open function follows this configuration, and then feeds the VISA Resource Name Out into a while loop where a VISA Read function displays the data in read buffer. Byte count for the VISA Read is set to 20 so I can read more of the erroneous datat, however actual data will only be 6-12 bytes. The while loop has a wait function, and no matter how much I slow down the readings I still get incorrect data (I have tried 20ms thru 1000ms).
The data I expect to receive in the read buffer from VISA Read is in the form of "0-255,0-255,0-255\n", like the following:
51,93,31\n
or
51,193,128\n
And occasionally I receive this data correctly, however I intermittently (sometimes every couple reads, sometimes a couple times in a row) get incorrect readings like this:
51,1\n
51,193739\n
\n
51,1933,191\n
51,,193,196\n
51,1933,252
51,203,116203,186\n
Where it seems like the read data is truncated, missing characters, or has additional characters. Looking at these values, however, it seems like the read was done incorrectly because the bytes seem partially correct (51 is the first number even in incorrect reads).
I have search but haven't found a similar issue and I am not sure what to try from here on. Any help is appreciated. Thanks!
Attachments:
Serial_Read_debugging.vi ‏13 KB

The first thing is that none of the error clusters are connected so you could be getting errors that you are not seeing. Are you sure about the comm parameters? Finally, I have never had a lot of luck looking for termination characters. You might want to just capture data and append each read into one long string just to see if you are still seeing this strangeness.
What sort of device is returning the data? How often does it spit out the data? How much distance is there between it and your computer? Can you configure it append something like a checksum or crc to the data?
Mike...
Certified Professional Instructor
Certified LabVIEW Architect
LabVIEW Champion
"... after all, He's not a tame lion..."
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Increase speed visa read write

Hi guys,
I am using the visa read and write example, but I am facing some issue when using it in a larger software, and I can only receive date when the vi has been slown down (using the lightbulb).
The programme definitely works on it own with the settings defined.
Therefore, do you have any ideas/suggestions on how to increase the speed of this vi (attached) significantly? Also, it seems to create an issue with the data read
Many thanks,
Kentmey
Kentmey
Solved!
Go to Solution.
Attachments:
Read and write.vi ‏22 KB

How are you using this code inside of another VI? If you are actually calling this VI, there needs to be some changes.
1. The port should only be initialized once at the beginning of your program and clsoed once at the end.
2. There shouldn't be any need for the bytes at port. You are set up to use a termination character. So just set the number of bytes to read to something really large (like 50 or 100) and let the VISA Read stop when it finds the termination character.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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Read in Binary form in VISA read function

Dear All,
I have connected my Device to the serial Port. and data read from the buffer is stored in text format. I want to view the data in binary format .
Actually, i have performed the same function in Visual Basic. there also if i view the data in text format, it shows some junk values. but if i view the data in binary, it shows the actual data coming from the instrument .
I dont know how to modify the VISA read function. can any one pls tell me how can i read the data in binary format?
Thanks
Ritesh

Oops! No it didn't.
Lab VIEW 2012 (if that makes a dif)
I'm using the VISA Read function to take ADC readings in from a microcontroller. The VISA Read function outputs the data as a string. Easy to convert the string to U8, either with the conversion function or type cast function, and works great except for a tiny corner case when the ADC reading is zero. The VISA Read function treats the 8-bit zero reading as a null character and strips it out.
Apparently, since this is done by the VISA Read function as it's building the string, type casting and or converting the output string from the VISA Read function doesn't "bring the zeros back".
I've tried setting the VISA property "Discard NUL Characters" to false, and that didn't seem to help.
My current work around is just to never have the micro send a zero ADC reading.
Anyway, I'm a Lab VIEW noob, so while this isn't essential to my project, I remain curious about how to send Lab VIEW serial data that isn't automatically considered characters, thrown into a string with all the zeros stripped out.
Regards,
Who

How do I avoid Error 85 in Scan From String scanning VISA read buffer?

I have encountered an Error 85 with my Scan From String VI. I have a timed
loop to read data from a device (flowmeter) using a serial port. This device takes
periodic measurements and sends the reading which contains a numerical value to the serial port COM1. It cannot be read continuously, and the period
between measurements may vary, so I decided a timed loop would be better than a while loop.
The VI begins with VISA Configure Serial Port and then
goes to a VISA Write which sends the message to the device to begin
taking measurements. After this, the device usually says "TAKE FLOWMETER READINGS" to the terminal, thereafter only sending numbers. Then begins my timed loop containing VISA Read. I
am taking the read buffer two places.
First, I am taking it to an Array to Spreadsheet String with the
Format String %.3f, as was in the Write to Text File example. Then I am
using Concatenate Strings with this string and also a string containing
the System Time. This string goes to Write to Text File, which I have
configured using Open/Create/Replace File outside of the loop.
Second, I am taking the read buffer to a waveform chart. I thought
it would be a good idea to use Scan From String to convert the string
into a DBL which I am then sending to the waveform
chart.
I am not sure if the initial "TAKE READINGS" message is giving me an error. I was able to get one reading saved to my text file from the device.
Also the format string for my Scan From String is %.3f
I am getting the Error 85 at the Scan From String only sometimes.
When this happens, there is no data being written to the text file. But
other times, I get data and it writes to the text file just fine (but
rounds to nearest whole number).
Any help would be greatly appreciated! This serial port device has been giving me a lot of trouble.

Is this what you mean? Did I wire the shift registers correctly?
I didn't know if you meant to Concatenate before Scan From String or Concantenate before or after VISA Read?
Message Edited by YeungJohn on 11-20-2008 03:48 PM
Message Edited by YeungJohn on 11-20-2008 03:49 PM
Attachments:
SerialShiftVI.JPG ‏87 KB

Configure VISA Read to terminate on unique character sequence

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