Hi Paul,
The shots were extracted from video of the UNO while my laser cutter was running. The serial transfer is a very simple polling scenario.
- The VB app sends a command string, and waits for an 'OK' from the Arduino
- Arduino catches the string and parses the variables <- RX flashes
- Arduino carries out motor/laser commands
- Arduino finishes and sends 'OK' back to the VB app <- TX flashes
And so on...
The photos show that the stalling is a fault with the Arduino or its code because the TX does not flash at the moment of stall (the last photo). Thus no 'OK' gets returned to VB. I had assumed for ages that VB/Windows was locking the port for some reason and not receiving the 'OK'.