Setting the RS-232 Transceiver Mode with DeviceIoControl

There are two ways to set and retrieve the RS-232 transceiver state:

• Set and read the NI-VISA wire mode attribute.
• The NI-Serial software uses programmatic control codes and the DeviceIoControl Windows function to retrieve the RS-232 transceiver state.

To set and retrieve the RS-232 transceiver state 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 TRANSCEIVER_MODE attribute can have the following values:
   • RS232_MODE_DTE
   • RS232_MODE_DCE
   • RS232_MODE_AUTO
   
   
   
   
3. To set the RS-232 transceiver, use NISERIAL_SET_RS232_MODE and DeviceIoControl. For example, to set to Force DCE mode, use the following code:

   TRANSCEIVER_MODE l_TransceiverMode = RS232_MODE_DCE;
   DWORD            l_ByteCount;
   
   DeviceIoControl (
      PortHandle,
      NISERIAL_SET_RS232_MODE,
      (LPVOID) &l_TransceiverMode,
      sizeof (l_TransceiverMode),
      (LPVOID) NULL,
      0,
      (LPDWORD) &l_ByteCount,
      NULL
      );

4. To retrieve the current RS-232 transceiver mode, you can use NISERIAL_GET_RS232_MODE and DeviceIoControl with the following code:

   TRANSCEIVER_MODE l_TransceiverMode;
   DWORD            l_ByteCount;
   
   DeviceIoControl (
      PortHandle,
      NISERIAL_GET_RS232_MODE,
      (LPVOID) NULL,
      0,
      (LPVOID) &l_TransceiverMode,
      sizeof (l_TransceiverMode),
      (LPDWORD) &l_ByteCount,
      NULL
      );