| 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).
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. |
This return value is zero if successful. Otherwise, it is negative if the fcn parameter does not specify a valid function code.
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.