Serial VISA operation does not work while PC Software does

Question

Hello everyone.
I am using LabVIEW to communicate with a control box via VISA Serial. I can communicate with this control box in most areas just fine, like the data monitoring function which I use without any problems. The one thing I'm having trouble with is calibrating the unit. Calibration is done by opening a binary file and transferring the data 16 bytes at a time over serial using a 16 byte write command, which has this structure: [Command, in this case "P"][2 byte address starting at 3800 HEX][16 bytes of data][1 byte checksum]. I am calculating the checksum correctly, and documentation says that the box should respond to any command within 100 milliseconds.
When I  attempt to do this, the box responds with an E several times (E is supposed to mean checksum error, even though I'm correctly calculating it), then stops responding to anything at all. The weird thing is that this box comes with software that can calibrate it and that software has no problems with it!
I tried using SuperMon to capture what the software sends over serial and compare it to what I send, and from what I can see, it sends the same data that I do, only it works and mine doesn't. I also tried using SuperMon to manually send the calibration one 16 byte write function at a time, and it seems to have the same problem.
It seems because their software works, I must be doing something wrong. Here's a screen shot of my code that I'm trying to use. Any help would be greatly appreciated!
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Answer 1

lukepike wrote:
Could you explain what you mean a little more? I never thought about that, I tried byte-swapping the whole command string right before I wrote it to the port, that didn't work. I also tried just byte-swapping the data only and nothing else, still no go.
I had another look at the NI Spy data, and it seems that some hex values are unprintable, maybe this is why they don't show up in the ascii part of the property window.
That's exactly what I meant.  Hmmm, the serial port is config'd the same way it is for the parts of the code that work?  Maybe there's a framing issue so the data is offset and the UUT sees it as garbage?
Bill
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