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LONG  cextfcn(cid, fcn);
int cid;
int fcn;
 
The cextfcn function carries out the extended communications function
specified by the fcn parameter. USER calls this function when an application
calls the EscapeCommFunction function (USER.214).
 
Parameter  Description
────────────────────────────────────────────────────────────────────────────
 
cid        Identifies the communications device.
 
fcn        Specifies the extended function to carry out. It can be one of
           the following values.
 
           Value       Meaning
           ─────────────────────────────────────────────────────────────────
           CLRDTR      Clears the data-terminal-ready (DTR) signal.
 
           CLRRTS      Clears the request-to-send (RTS) signal.
 
           GETBASEIRQ  Returns the base-port address and IRQ setting for the
                       COM port specified by the cid parameter. The low 16
                       bits of the return address specifies the base-port
                       address, and the high address specifies the IRQ
                       selection. If the high 16 bits is -1, then the port
                       does not exist; if it is zero, the installed COMM
                       driver does not support this escape.
 
           GETMAXBAUD  Returns a constant that indicates the highest baud
                       rate supported by the port specified by the cid
                       parameter. The following constants may be returned.
 
                       Value       Meaning
                       ─────────────────────────────────────────────────────
                       CBR_110     The highest baud rate is 110.
 
                       CBR_300     The highest baud rate is 300.
 
                       CBR_600     The highest baud rate is 600.
 
                       CBR_1200    The highest baud rate is 1200.
 
                       CBR_2400    The highest baud rate is 2400.
 
                       CBR_4800    The highest baud rate is 4800.
 
                       CBR_9600    The highest baud rate is 9600.
 
                       CBR_19200   The highest baud rate is 19,200.
 
                       CBR_38400   The highest baud rate is 38,400.
 
                       CBR_56000   The highest baud rate is 56,000.
 
                       CBR_128000  The highest baud rate is 128,000.
 
                       CBR_256000  The highest baud rate is 256,000.
 
           GETMAXCOM   Returns the maximum COM port identifier supported by
                       the communications driver. This value ranges from
                       0x00 to 0x7F, such that 0x00 corresponds to COM1,
                       0x01 to COM2, 0x02 to COM3, and so on. The
                       communications driver included in Windows 3.1
                       supports COM1 through COM4, and will always return
                       0x03.
 
           GETMAXLPT   Returns the maximum LPT port ID supported by the
                       system. This value ranges from 0x80H to 0xFFH, such
                       that 0x80H corresponds to LPT1, 0x81H to LPT2, 0x82H
                       to LPT3, and so on.
 
           RESETDEV    Resets the printer device (that is, assert the reset
                       line) if the cid parameter specifies an LPT port. No
                       function is performed if cid specifies a COM port.
 
           SETDTR      Sets the data-terminal-ready (DTR) control line on.
 
           SETRTS      Sets the request-to-send (RTS) control line on.
 
           SETXOFF     Causes transmission to act as if an XOFF character
                       has been received.
 
           SETXON      Causes transmission to act as if an XON character has
                       been received.
 
Return Value
 
This return value is zero if successful. Otherwise, it is negative if the
fcn parameter does not specify a valid function code.
 
Comments
 
The export ordinal for this function is 9.
 
If the communications driver does not export the CommWriteString function,
Windows 3.1 intercepts and adjusts the return values for the GETBASEIRQ,
GETMAXBAUD, GETMAXLPT, and GETMAXCOM functions after the cextfcn function
returns.
 
Updates/Changes
 
The cextfcn function now returns a 32-bit value and accepts the new
communication escapes RESETDEV, GETMAXLPT, and GETMAXCOM.
 
 
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