COM Statements


 Action

 Enable, disable, or suspend event trapping at the COM port.


 Syntax

  COM( n%)  ON
  COM( n%)  OFFn%)
  COM( n%)  STOP


 Remarks

 The argument  n% specifies the number of the COM (serial) port;  n% can be
 either 1 or 2.

  COM( n%)  ON enables communications-event trapping on COM port  n%. If a
 character arrives at a communications port after a  COM( n%)  ON statement,
 the routine specified in the  ON  COM statement is executed.

  COM( n%)  OFF disables communications-event trapping on COM port  n%. No
 communications trapping takes place until another  COM( n%)  ON statement is
 executed. Events occurring while trapping is off are ignored.

  COM( n%)  STOP suspends communications-event trapping on COM port  n%. No
 trapping takes place until a  COM( n%)  ON statement is executed. Events
 occurring while trapping is suspended are remembered and processed when the
 next  COM( n%)  ON statement is executed. However, remembered events are
 lost if  COM( n%)  OFF is executed

 When a communications-event trap occurs (that is, the  GOSUB operation is
 performed), an automatic  COM( n%)  STOP is executed so that recursive traps
 cannot take place. The  RETURN statement from the trapping routine
 automatically executes a  COM( n%)  ON statement unless an explicit  COM(
 n%)  OFF was performed inside the routine.

 For more information, see Chapter 9, "Event Handling" in the  Programmer's
 Guide.


 See Also

  ON  event


 Example


 The following example opens COM1 and then monitors the COM1 port for input.
 It uses the  ON COM statement to trap communications events.

 CLS
 ' Set up error handling in case COM1 doesn't exist.
 ON ERROR GOTO ErrHandler
 OPEN "COM1.9600,N,8,1,BIN" FOR INPUT AS #1

 COM(1) ON ' Turn on COM event processing.
 ON COM(1) GOSUB Com1Handler' Set up COM event handling.
 ' Wait for a COM event to occur or a key to be pressed.
 DO . LOOP WHILE INKEY$ = ""
 COM(1) OFF' Turn off COM event handling.
 CLS
 END

 Com1Handler.
     PRINT A$; "Something was typed on the terminal attached to COM1."
     RETURN

 ErrHandler.
     SELECT CASE ERR
         CASE 68. PRINT "COM1 is unavailable on this computer.". END
         CASE ELSE. END
     END SELECT