National Instruments PCI-8430, Manual

Page: 114 / 237

Setting the RS-485 Programmatically Controlled Bias
Resistors with DeviceIoControl
The NI-Serial software uses programmatic control codes and the
DeviceIoControl Windows function for programming the RS-485 bias
resistor mode. To set and retrieve the RS-485 bias resistor mode,
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_RS485_BIAS
attribute can have the following values:
RS485_BIAS_OFF
RS485_BIAS_ON
3. To set the RS-485 bias resistor mode, use
NISERIAL_SET_RS485_BIAS
and DeviceIoControl. For example,
to enable programmatically controlled RS-485 bias resistors, use
the following code:
SERIAL_RS485_BIAS l_SerialRs485Bias = RS485_BIAS_ON;
DWORD l_ByteCount;
DeviceIoControl (
PortHandle,
NISERIAL_SET_RS485_BIAS,
(LPVOID) &l_SerialRs485Bias,
sizeof (l_SerialRs485Bias),
(LPVOID) NULL,
0,