100 MHz, 54 Single-Ended-Channel Digital I/O Adapter Module for FlexRIO—The NI-6581 is a digital I/O adapter module that, when combined with a PXI FPGA Module for FlexRIO, creates a digital instrument for interfacing with 54 single-ended digital pins. You can use the NI-6581 to do real-time interfacing of standard protocols and implement customized protocols. The NI-6581 can operate sample digital waveforms at up to 100 MHz. It includes support for common transistor-to-transistor logic (TTL) voltage levels, or other voltage references can be sourced externally using a front panel connector.