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Auxiliary Digital I/O Ports

The USRP motherboard has high speed 64 bit digital I/O ports. These are divided in two groups (32 bit for IO_RX and 32 bit for IO_TX). These digital I/O pins are connected to the daughterboards interface connecters (RxA, TxA, RxB and TxB). Each of these connectors has 16 bit digital I/O bits. These signals can be controlled from software by reading/writing to special FPGA registers and each can be independently configured either as digital input or digital output.

Some of these pins are used to control specific operations on the installed daughterboards such as controlling the selection of receiving RF input port, in automatic transmit/receive mode, controlling power supply feeding for different TX and RX parts, synthesizer lock detection,…etc. It can be also used to implement AGC processing and can be very helpful in debugging FPGA implementations when connected to a logic analyzer.

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