Serial Basic Hookup Guide

Contributors: Nate
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Serial Basic Overview

The pinout of the Serial Basic mimics the common DTR/RX/TX/VCC/CTS/GND pinout found on hundreds of FTDI-to-USB derivatives.

Top of Serial Basic CH340G

Pin LabelInput/OutputDescription
DTROutputData Terminal Ready, Active Low
RXIInputSerial Receive
TXOOutputSerial Transmit
VCCSupply OutputPower supply 3.3V (default) or 5V
CTSInputClear To Send, Active Low
GNDSupply OutputGround (0V) supply

Alignment Markers

These GRN and BLK indicators are there to help you align the board properly with products that use this same pinout.

Alignment markers on Serial Basic

The Serial Basic mates seamlessly with products that use the standard serial connection. If you see a board with the BLK and GRN labels, then you know it will be compatible with the Serial Basic.

nRF52832 Breakout

See the GRN and BLK labels on this nRF52832 Breakout?

Where did GRN and BLK come from? Way back in 2008, when we created the Arduino Pro Mini, we needed to have a pinout to allow serial bootloading. At the time, the best USB to TTL Serial device was the FT232 Cable. Its unpolarized connector could be flipped either way so we added the words GRN and BLK to the PCB to let folks know how to line up the colored wires. The practice stuck! Now, many boards use this standard.

The old FTDI Cable

The cable with colored wires

Voltage Selection Jumper

There is a jumper on the rear of the board that controls the output voltage on the VCC pin. By default, the board outputs 3.3V and has 3.3V signals. Changing this jumper to 5V will cause the board to output 5V on the VCC pin with 5V signals.

Jumper to select between 3.3V and 5V

Jumper is default to 3.3V VCC and I/O

When the jumper is set to 3.3V, the board uses an onboard 3.3V regulator capable of sourcing 600mA. If you attempt to pull more than 600mA, the regulator will go into short-circuit shutdown where it will only output 150mA.

When the jumper is set to 5V, the board will source as much power as your USB port will provide.


There are two LEDs on the board connected to TX (Green) and RX (Yellow). This is a quick and handy way to see the serial traffic.

LEDs on CH340G Serial Basic