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Old February 8th, 2018, 07:21 AM   #1
FactoryTalktotheHand
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Troubles with 1769-ASCII and Labview

Working with a customer who wants to do some ASCII handshaking between the PLC (a 1769-L24ER) and Labview on a laptop. I can send data from the PLC just fine, but for some reason, when Labview sends an acknowledgement back, the ASCII module doesn't get it.

He has a serial port sniffer program up when he does this and it does send data. After some working last night, I was able to get a transmission from the Laptop to the ASCII module working, but only via YAT, a terminal program. We looked at the hex values being sent with the sniffer, and there's nothing about what YAT sends that looks any different than what Labview is sending, but clearly since YAT is working and Labview isn't, something is different.

I've tried every setting combination in the ASCII module. My baud rates are right. The code I'm using is the A-B sample code rung for rung.

I know absolutely nothing about Labview and I don't really want to. What puzzles me though is that Transmitting works with YAT but not with Labview, but Labview can receive a line just fine.
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Old February 8th, 2018, 08:02 AM   #2
shawn_75
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I'd start with a loopback cable on the serial port. Transmit your data on the loopback using both LabView and YAT. See if they are the same.
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Old February 8th, 2018, 08:03 AM   #3
Mispeld
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Is Labview sending a delimiter (e.g., carriage return) character to signal end of transmission? If so, and you are using a 1734-232ASC module, you will want to define the specific delimiter on the Configuration tab in the Receive Data frame. If not, I expect the program will need to be set up for a fixed length transmission.
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Old February 8th, 2018, 05:25 PM   #4
Highland Controls
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As Mispeld pointed out, this is likely a termination character issue. LabVIEW doesn't send a termination character by default. It need to be appended programmatically. The YAT program is probably sending CR/LF when you hit the Enter button.
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Old February 8th, 2018, 05:34 PM   #5
Highland Controls
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Don't let the LabVIEW programmer tell you he is sending the termination character because he has it selected in the Configure Serial Port VI. That is only used for reading data.
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