National Instruments PCI-8430 - Page 113

SettingtheUSB-485Programmatically
ControlledBiasResistorMode
TheUSB-485hardwarecanprogrammaticallycontroltheonboard
(nonsocketed)biasresistors.Bydefault,theseresistorsareenabled
duringnormaldeviceoperationanddisabledduringUSBsuspend.There
aretwowaystocontroltheseresistors:
UsetheAdvancedtabinMAX.IftheEnableDynamicBias
Resistorsboxischecked,theresistorsareenabledautomatically
wheneveraserialportisopenduringnormaloperation.Ifthebox
isnotchecked,theresistorsaredisabled.
Yoursoftwarecanenableordisablethebiasresistors
programmaticallybymakingDeviceIoControlcallstotheserial
driver.