@Tim H This is going to slow down over time, which could account for part of what you're seeing. Try using
My recommendation, though, would be to not leave anything in the serial buffer. Get it all out with readall, append it to an internal buffer and be done. Spend as little time as possible in DataAvailable. Use a timer to process the buffer and stuff it into your textfield.
Good idea! As a test, I just ReadAll and displayed it over and over, building nothing longer. It behaves the same way. The first string has the real data, the second string and from then on contains the same 00 E0 data.
Can it be that Xojo is unable to keep up with a fast data feed? I would think that the buffer would allow this.