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!

I contacted the makers of the control box and have solved the issue. The control box needs a 5-10 millisecond delay between every byte, not every command as I had originally thought. Thanks for all the helpful replies, and especially the split number tip, that really cleans up my code!