Deal All, I am designing a form with a listbox and two command bottons, one for starting a loop of measurement, the other for interrupting the measurement. When the button of starting measurement, a do loop is the activated, and continue reading signal from rs232 port. outputing the signal to the listbox. The other botton is used for ending the loop. What I hope is no matter I press ESC key or the botton, the loop will be stopped. The program I wrote as follows, ======= *** When command button cmbtStartMeasure is clicked, starting measuring action ** Step 1, open the port for receving data If ThisForm.Comm.PortOpen=.F. ThisForm.comm.portopen=.T. Endif ** Step 2, Starting a loop reading data, until ESC is pressed * Looping * If ESC is pressed, * then stoping measuring * Otherwise: * Checking whether the data in the input buffer * reaches 13, which is the standard length * of a piece of measurementthen * Read data and show it in the EditBox, OutputData * End Looping Do while .T. If ESC_PRESSED=.T. EXIT ENDIF If ThisForm.comm.InBufferCount>=13 ThisForm.DataOutput.additem(ThisForm.comm.Input) ThisForm.refresh Endif ENDDO ** Step 3: Close the port IF ThisForm.Comm.PortOpen=.T. ThisForm.comm.portOpen=.F. ENDIF =messagebox("stoping measurement, µ²§ô¶q´ú",0,"") ========= And the code for the other botton as follows, ========= IF ThisForm.Comm.PortOpen=.T. ThisForm.comm.PortOpen=.F. && Close the port ENDIF =messagebox("stoping measurement, µ²§ô¶q´ú",0,"") ThisForm.Release Another procedure I wrote for this form, in the keyPress event follows which sensors whether ESC is pressed for stoping the loop. LPARAMETERS nKeyCode, nShiftAltCtrl * When Escape Key is pressed, stoping measuring reading If nKeyCode=27 && ESC pressed ESC_PRESSED=.T. ENDIF However, each time when I run it, I cannot stop the by clicking on the second botton. Especially, when there is no signal from the comm port, the loop seems no ending. When I press the ESC key, one message shows to interrupt the program, but doesn't seem caused by the procedure I wrote. Can someone check for me, and give me some suggestion. Many thanks in advance, and looking forward for replies. Best regards, Ron.