Setting the RS-485 Transceiver Control Mode in Windows

Setting the Default Mode of Operation

To set the default mode of operation:

• Use the Advanced tab in Measurement & Automation Explorer (MAX).

Modifying the RS-485 Transceiver Mode Programmatically

To modify the RS-485 transceiver mode programmatically:

• Change the NI-VISA wire mode attribute.
• The NI-Serial software uses programmatic control codes and the DeviceIoControl Windows function for programming the RS-485 transceiver control mode.

  Setting the RS-485 Transceiver Control Mode on PCI, PXI, USB, ExpressCard, and PCMCIA Hardware

  To set and retrieve the RS-485 transceiver control mode using the DeviceIoControl Windows function on PCI, PXI, USB, ExpressCard, and PCMCIA RS-485 hardware, complete the following steps:
  
  
  
  1. Add the following lines to your source code:

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

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

  2. The TRANSCEIVER_MODE attribute can have the following values:
     • RS485_MODE_4WIRE
     • RS485_MODE_2W_ECHO
     • RS485_MODE_2W_DTR
     • RS485_MODE_2W_AUTO
     
     
     
     
  3. To set the RS-485 transceiver control mode, use NISERIAL_SET_RS485_MODE and DeviceIoControl. For example, to set to two-wire Auto Control mode, use the following code:
     
     

     TRANSCEIVER_MODE l_TransceiverMode = RS485_MODE_2W_AUTO;
     DWORD            l_ByteCount;
     
     DeviceIoControl (
        PortHandle,
        NISERIAL_SET_RS485_MODE,
        (LPVOID) &l_TransceiverMode,
        sizeof (l_TransceiverMode),
        (LPVOID) NULL,
        0,
        (LPDWORD) &l_ByteCount,
        NULL
        );
     

  4. To retrieve the current RS-485 transceiver control mode, you can use NISERIAL_GET_RS485_MODE and DeviceIoControl with the following code:
     
     

     TRANSCEIVER_MODE l_TransceiverMode;
     DWORD            l_ByteCount;
     
     DeviceIoControl (
        PortHandle,
        NISERIAL_GET_RS485_MODE,
        (LPVOID) NULL,
        0,
        (LPVOID) &l_TransceiverMode,
        sizeof (l_TransceiverMode),
        (LPDWORD) &l_ByteCount,
        NULL
        );

  Setting the RS-485 Transceiver Control Mode on ENET Hardware

  To set and retrieve the RS-485 transceiver control mode using the DeviceIoControl Windows function on ENET RS-485 hardware, complete the following steps:
  
  
  
  1. Add the following lines to your source code:

     #include <winioctl.h>
     #define SERIAL_TM_4WIRE	0x80
     #define SERIAL_TM_2W_ECHO	0x81
     #define SERIAL_TM_2W_DTR	0x81
     #define SERIAL_TM_2W_AUTO	0x83
     #define IOCTL_SERIAL_SET_TRANSCEIVER_MODE
        CTL_CODE(FILE_DEVICE_SERIAL_PORT,37,METHOD_BUFFERED,FILE_ANY_ACCESS)
      

  2. To set the RS-485 transceiver control mode, use IOCTL_SERIAL_SET_TRANSCEIVER_MODE and DeviceIoControl. For example, to set to two-wire Auto Control mode, use the following code:

     ULONG bytecount;
     TRANSCEIVER_MODE transceiver_mode = SERIAL_TM_2W_AUTO;
     DeviceIoControl(
        comhandle,
        IOCTL_SERIAL_SET_TRANSCEIVER_MODE,
        (PVOID) &transceiver_mode,
        sizeof(transceiver_mode),
        (PVOID) NULL, 0,
        &bytecount,
        NULL
     );