How To Use the OpenComm() Function with FOXTOOLS.FLL

• Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b, 2.6, 2.6a

SUMMARY

OpenComm() is a function that can be called using FOXTOOLS.FLL to open the COM or LPT ports. Below is a complete description of OpenComm().

MORE INFORMATION

Purpose

The OpenComm() function opens a communications device.

Function Syntax

   OpenComm(<port>, <in_q>, <out_q>)

   Argument       Description
   -----------------------------------------------------------------

   <port>         Points to a null-terminated string that specifies
                  the device in the form COM<n> or LPT<n>, where <n>
                  is the device number.

   <in_q>         Specifies the size, in bytes, of the receiving
                  queue. This parameter is ignored for LPT devices.

   <out_q>        Specifies the size, in bytes, of the transmission
                  queue. This parameter is ignored for LPT devices.

Returns

The return value identifies the open device if the function is successful. Otherwise, it is less than zero.

Errors

If the function fails, it may return one of the following error values:

   Value     Meaning
   --------------------------------------------------------------------

   -12       The device's baud rate is unsupported.
   -11       The specified byte size is invalid.
   -10       The hardware is not available (is locked by another device).
    -5       The default parameters are in error.
    -4       The function cannot allocate the queues.
    -3       The device is not open.
    -2       The device is already open.
    -1       The device identifier is invalid or unsupported.

Comments

Windows allows COM ports 1 through 9 and LPT ports 1 through 3. If the device driver does not support a communications port number, the OpenComm() function will fail.

Sample Code

The following code example uses the OpenComm() function and FOXTOOLS.FLL to open COM1. (This example can be found in FOXPROW\GOODIES\FOXTOOLS\DIALER.PRG.)

   *-------------------- dialer.prg ------------------------

   * Sample program to output to comm port
   * Uses FoxTools library for generic DLL access

   SET LIBRARY TO SYS(2004)+"foxtools.fll" ADDITIVE

   opencomm = REGFN("OpenComm", "CII", "I")
   writecomm = REGFN("WriteComm", "ICI", "I")
   closecomm = REGFN("CloseComm", "I", "I")

   com1 = CALLFN(opencomm, "COM1:", 100, 100)
   s = "ATDT 5551212" + chr(13)
   =CALLFN(writecomm, com1, s, len(s))

   WAIT WINDOW "Press any key to hang up"
   s = "ATH0" + chr(13)
   =CALLFN(writecomm, com1, s, len(s))

   =CALLFN(closecomm, com1)

   RELEASE LIBRARY SYS(2004)+"foxtools.fll"

   hnd = RegFN("OpenComm","CCC","I","User.dll")

REFERENCES

The above information can also be found in the Microsoft Windows Software Development Kit (SDK) "Programmer's Reference Volume 2: Functions" [describes OpenComm()] and the "Programmer's Reference Volume 3: Messages, Structures, and Macros" (describes the returned values). The online Help file for the Professional Version of Visual C++ also contains this information.