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You can programmatically set the NI 6555/6556 generation channels (DIO <0..23>) to a tristate condition through the following mechanisms:
|Note During power up and reset, these channels are put in a high-impedance state.|
When a channel is tristated, you can use the Tristate Mode property or the NIHSDIO_ATTR_DATA_TRISTATE_MODE attribute either to put the output terminal in a high-impedance state or to terminate the channel to a tristate voltage level (VTT) through 50 Ω. This VTT level should be the same level used for the Termination Mode property or the NIHSDIO_ATTR_DATA_TERMINATION_MODE attribute, if you use both properties in your application. Refer to the input impedance topic for more information about VTT.
Termination and tristate voltage (VTT) is a third driver voltage level with all the same restrictions and performance as the Generation Voltage High (VOH) and Low (VOL) Levels, including range and source impedance specifications, that you can configure on a per channel basis. Refer to the NI PXIe-6555/6556 Specifications for details about the specifications for VTT.
|Note Although VTT is supported in acquisition and generation sessions, the generation session refers to the setting as tristate voltage, while the acquisition session refers to the setting as termination voltage. Refer to the Tristate Mode and Termination Mode properties or the NIHSDIO_ATTR_DATA_TRISTATE_MODE and NIHSDIO_ATTR_DATA_TERMINATION_MODE attributes for more information about how to configure VTT in NI-HSDIO.|