The USRP E320 implements an 8-bit GPIO port. Each bit is routed to a dedicated pin in the Zynq PL. The GPIO port uses a mini-HDMI (HDMI Type C) jack on the E320 back panel.

The 802.11 MAC/PHY design uses the GPIO port for debug I/O. The GPIO pins are connected to the wlan_userio core which implements the necessary logic to use each GPIO pin as an input or output. The wlan_userio core supports reading GPIO inputs from software or hardware, and supports setting GPIO outputs from software or hardware. By default the 8 GPIO pins are configured as software-controlled outputs.


The USRP E320 hardware connects the 19 pins of the mini-HDMI jack to the 8 GPIO signals plus ground and power. The table below lists the E320 nets connected to each mini-HDMI pin, and the corresponding pin number when a mini-HDMI (Type C) to HDMI (Type A) adapter is used.

The GPIO_n signals are 3.3v I/O. The direction (input/output) is configured per-pin in the 802.11 MAC software.

E320 Net mini-HDMI Pin (Type C) HDMI Pin (Type A)
GPIO_0 8 7
GPIO_1 9 9
GPIO_2 11 10
GPIO_3 12 12
GPIO_4 14 13
GPIO_5 15 15
GPIO_6 16 16
GPIO_7 17 14
GND 1 2
GND 3 3
GND 4 5
GND 6 6
GND 7 8
GND 10 11
GND 13 17
GND 19 19
+3.3v 18 18
2 1
5 4

802.11 Debug Outputs

The 802.11 MAC/PHY design drives real-time MAC and PHY status signals to debug outputs. On hardware platforms with debug headers these status outputs can be probed with an oscillosope to observe MAC/PHY state in real-time.

The reference 802.11 FPGA design for the USRP E320 connects the 8 LSB of the MAC/PHY debug bus to the E320 GPIO port. Observing these signals with a scope requires external equipment to access the GPIO pins.

Cable Recommendations

To observe MAC/PHY debug signals we recommend using a cable and breakout board to access the GPIO signals:

Other combinations should work, like a mini-HDMI to HDMI adapter and an HDMI plug breakout (

In both cases the HDMI breakout boards enumerate pins using the Type A connector pin numbers. Refer to the table above for the mapping of Type A pins to USRP E320 GPIO signals.

An oscilloscope probe ground lead can use the HDMI pins tied to ground (GND in the table above) on the E320 board.