waituntil alternative in LabVIEW

[Marc_A]

I don't mean to be picky Dennis, but the code you posted won't work if it takes longer than a VISA timeout to read the 'A'. If the VISA read times out, it will generate an error which will be sent to the shift register. Now the next time through the loop, the read won't even execute because it will see an error in.

[Dennis_Knutson]

You're right. I have no idea how long it would take for the instrument to send the character but the best thing would be to put a VISA Bytes at Serial Port before the read and if bytes are greater than 0, do the read inside a case statement.

Message Edited by Dennis Knutson on 01-16-2007 12:16 PM

[maple72]

Hi

I have some questions regarding your program you sent me , I have  taged to questions ( labled them on there graph) could you answer them to me Please

Thanks....

Maple

[maple72]

the screenshot is attched

[maple72]

Hi Dennis

Thnaks alot for your help , does your program wait unti it recives an serial port Character B, ? I have some questions about the program that are labled with the graph of the program you gave me and it is attached to my post could you answer me them please

Thanks

Maple

[Dennis_Knutson]

As the on-line help explains, VISA Bytes at Serial Port reads the number of bytes in the serial buffer and returns that value. If the value is greater than 0, a read is done. If the string returned contains the character 'B', then the while loop stops.

[maple72]

Dear Deninis

Thanks alot for your help, I will attach for you  a screenshot of the program you sent it , just asking when the case structure is false is this a proper wiring I have done , also to stop the loop what shall I wire to it ,

Thanks

[Dennis_Knutson]

Since you said you want the while loop to run until the character is detected, the false case would have a False constant inside it. You could also right click on the exit tunnel and select Use Default if Unwired. The default is False but I usually prefer to explicitly provide a value.

Stopping a while loop and passing values through case statements are pretty basic elements in LabVIEW. I t sounds like you are just beginning so you might want to look at the resources available for learning LabVIEW at http://zone.ni.com/devzone/cda/tut/p/id/5199.

[napview]

You may need to spend more time playing around with the serial port. After all we learn from our mistakes.

[Dennis_Knutson]

Since you are not using a shift register for the error cluster, you probably don't need to check for an error condition and remove it. It's not very likely that an error would occur on a write anyway and if it did, you would probably want to detect that and stop. Also, you can wire your error cluster to the case statement selector input. The case statement changes colors and shows an Error (red) and No Error (green) case.

Message Edited by Dennis Knutson on 01-17-2007 12:17 PM