Digital I/O

The NI USB-7856R provides connections for 48 digital input/output (DIO) channels. Connector 0 contains 32 high-speed DIO channels that can run up to 80 MHz signal frequencies and Connector 1 contains 16 low-speed channels that can run up to 10 MHz signal frequencies. Each connector has selectable logic levels that you can configure as 1.2 V, 1.5 V, 1.8 V, 2.5 V, or 3.3 V. You can configure each channel as input or output.

1. High-speed signal frequencies up to 80 MHz with logic levels configured as 1.2 V, 1.5 V, 1.8 V, 2.5 V, or 3.3 V.
2. Low-speed signal frequencies up to 10 MHz with logic levels configured as 1.2 V, 1.5 V, 1.8 V, 2.5 V, or 3.3 V.
3. LED

The DIO channels connect to the FPGA through buffers, which have overvoltage and undervoltage protection as well as over current protection. Refer to the NI USB-7856R Specifications for more information about the maximum voltage and current.

When the system powers on, the DIO channels are set as input low with pull-down resistors. To set another power-on state, you can configure the NI USB-7856R to load a VI when the system powers on. The VI can then set the DIO lines to any power-on state.

All the high-speed DIO channels on Connector 0 are routed with a 50 Ω characteristic trace impedance. Route all external circuitry with a similar impedance to ensure best signal quality. NI recommends performing signal integrity measurements to test the affect of signal routing with the cable and connection accessory for your application.