Setting Ring Indicate (RI) and Data Carrier Detect (DCD) with DeviceIoControl

There are two ways to set and retrieve these RS-232 signals:

• Set and read the NI-VISA Line RI State and Line DCD State attributes.
• The NI-Serial software uses programmatic control codes and the DeviceIoControl Windows function to retrieve these RS-232 signals.

To retrieve these RS-232 signals using the DeviceIoControl Windows function, complete the following steps:

1. Add the following lines to your source code:

   #include <winioctl.h>
   #include <NiSerial.h>

   Note  The header file NiSerial.h is included on your NI-Serial software CD. You also can find it in the NI-Serial folder where you installed your National Instruments software (typically, C:\Program Files\National Instruments\NI-Serial).

2. The SERIAL_RI_OUT attribute can have the following values:
   • SERIAL_RI_ON
   • SERIAL_RI_OFF
   
   
   
   
3. To set the RS-232 signal RI when the transceiver is in DCE mode, use the following code:

   DWORD l_ByteCount;
   
   DeviceIoControl (
      PortHandle,
      NISERIAL_SET_RI,
      (LPVOID) NULL,
      0,
      (LPVOID) NULL,
      0,
      (LPDWORD) &l_ByteCount,
      NULL
      );

4. To clear the RS-232 signal RI when the transceiver is in DCE mode, use the following code:

   DWORD l_ByteCount;
   
   DeviceIoControl (
      PortHandle,
      NISERIAL_CLR_RI,
      (LPVOID) NULL,
      0,
      (LPVOID) NULL,
      0,
      (LPDWORD) &l_ByteCount,
      NULL
      );

5. To retrieve the current state of the RS-232 signal RI when the transceiver is in DCE mode, use the following code:

   SERIAL_RI_OUT l_SerialRiOut;
   DWORD         l_ByteCount;
   
   DeviceIoControl (
      PortHandle,
      NISERIAL_GET_RI,
      (LPVOID) NULL,
      0,
      (LPVOID) &l_SerialRiOut,
      sizeof (l_SerialRiOut),
      (LPDWORD) &l_ByteCount,
      NULL
      );

6. The SERIAL_DCD_OUT attribute can have the following values:
   • SERIAL_DCD_ON
   • SERIAL_DCD_OFF
   
   
   
   
7. To set the RS-232 signal DCD when the transceiver is in DCE mode, use the following code:

   DWORD l_ByteCount;
   
   DeviceIoControl (
      PortHandle,
      NISERIAL_SET_DCD,
      (LPVOID) NULL,
      0,
      (LPVOID) NULL,
      0,
      (LPDWORD) &l_ByteCount,
      NULL
      );

8. To clear the RS-232 signal DCD when the transceiver is in DCE mode, use the following code:

   DWORD l_ByteCount;
   
   DeviceIoControl (
      PortHandle,
      NISERIAL_CLR_DCD,
      (LPVOID) NULL,
      0,
      (LPVOID) NULL,
      0,
      (LPDWORD) &l_ByteCount,
      NULL
      );

9. To retrieve the current state of the RS-232 signal DCD when the transceiver is in DCE mode, use the following code:

   SERIAL_DCD_OUT l_SerialDcdOut;
   DWORD          l_ByteCount;
   
   DeviceIoControl (
      PortHandle,
      NISERIAL_GET_DCD,
      (LPVOID) NULL,
      0,
      (LPVOID) &l_SerialDcdOut,
      sizeof (l_SerialDcdOut),
      (LPDWORD) &l_ByteCount,
      NULL
      );