> For the complete documentation index, see [llms.txt](https://brlabelectronics.gitbook.io/hardware-1/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://brlabelectronics.gitbook.io/hardware-1/functional-description/pin-screw-terminal-description.md).

# Pin/Screw Terminal Description

<table><thead><tr><th width="134"></th><th>Description</th></tr></thead><tbody><tr><td>+</td><td>This screw terminal position is connected to the positive leg of the 12V supply.</td></tr><tr><td>-</td><td>This screw terminal position is connected to the ground leg of the 12V supply.</td></tr><tr><td>5V</td><td>This screw terminal is a 5V output from the buck converter</td></tr><tr><td>3V3</td><td>This pin is the output of the 3.3V voltage regulator.</td></tr><tr><td>GND</td><td>Board ground pin and screw terminal.</td></tr><tr><td>A0-A5</td><td>Analog input pins that can also act as standard digital GPIO and are PWM capable.</td></tr><tr><td>D2-D4</td><td>Common GPIO pins that are PWM capable.</td></tr><tr><td>MO,MI,SCK</td><td>SPI pins. They can also be used as digital GPIOs.</td></tr><tr><td>RX</td><td>Primarily used as a UART RX pin, can also be used as a digital GPIO.</td></tr><tr><td>TX</td><td>Primarily used as a UART TX pin, can also be used as a digital GPIO.</td></tr><tr><td>SDA</td><td>Primarily used as a data pin for I 2C, can also be used as a digital GPIO.</td></tr><tr><td>SCL</td><td>Primarily used as a clock pin for I 2C, can also be used as a digital GPIO.</td></tr><tr><td>NO</td><td>Normally Open pin for the relay.</td></tr><tr><td>COM</td><td>Common pin for the relay.</td></tr><tr><td>NC</td><td>Normally Closed pin for the relay.</td></tr></tbody></table>


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