µVISION DEBUGGER: Assigned Com Ports Use XON/XOFF

Information in this article applies to:

• µVision Version 2.12

QUESTION

I'm using the µVision Debugger and I'm assigning my serial port to COM2 using the ASSIGN command. I connect COM2 to an external hardware device that sends data to my simulated program.

After a few characters are transmitted, the PC sends an XOFF character to my hardware. Why is that?

ANSWER

When you assign the simulated serial port to a PC's COM port, the µVision Debugger creates a 3.5K receive buffer for the characters received. Once the buffer fills-up, an XOFF character is sent so that received characters are not lost.

At this time, there is no way to disable this software flow control. However, this feature may be introduced in a future revision.

If the XON/XOFF characters are not supported by your protocol, you must slow down the speed of the PC's COM port so that the input buffer does not fill up.

Last Reviewed: Thursday, January 21, 2021