Serial Connection Tutorial: FTDI 232RL

A serial connection is necessary when troubleshooting (or installing) on a headless system (no display/monitor).


I have used a CH340 based USB Serial UART device and have had mixed results. That is why I use USB Serial UART devices based on FTDI's 232RL chip with 3.3v voltage or voltage selector. The version I use is this one:

This is another model that should have no problems: Notice that it features a "genuine" chip.

You can use cheaper USB Serial UART models but those most likely use imitation chips. This is not an issue if you use linux, but windows machines will brick models with fake FTDI chips. The knockoffs can be unbricked, but that is beyond the scope of this tutorial.

The RockPro64 UART RX/TX pins use 3V by default according to the schematics. ENSURE you set your USB Serial UART device to 3.3V.

  1. Do not use a knockoff FT232RL based USB Serial UART with a windows system, it will brick the device.
  2. Set your USB Serial UART device to 3.3V.
  3. You are responsible for all outcomes resulting from the result of this information, including letting the smoke out™.
Physical Connections

You will require a USB extension cable to connect the USB Serial UART to the host desktop/laptop/SBC. The type also depends on the USB connector on your USB Serial UART device. The USB extension cable needed for the devices I have linked to in this tutorial require a type A-Male to Mini-B cable similar to this: 

You will have to purchase jumper wires to connect the USB Serial UART to the RockPro64. I use MALE to FEMALE jumpers similar to these: The gender of your jumper wires will depend on the connectors on your USB Serial UART device.

Only 3 jumper wires are required. Verbally, GND (pin 6) to GND, TX (pin 8) to RX, and RX (pin 10) to TX are the connections made between the RockPro64 and the USB Serial UART device. Visually, it looks like this:

RockPro64        FT232RL USB Serial UART
=========        =======================

pin 6  *|--------|* GND
pin 8  *|---\    |* CTS
pin 10 *|-\  \   |* 5V
           \-----|* TXD
               \-|* RXD
                 |* DTR

Software Connection

On the linux host, I used picocom. If you are using a windows host, then putty is probably what you will use. This is what I ran on my host:

$ picocom -b 1500000 /dev/ttyUSB0


If you are not successfully communicating with the RockPro64 these are common things to check in order:
  1. Check for a disconnected wire
  2. Check that the wires are correctly connected
  3. Check that you are using the correct device (i.e. /dev/ttyUSB#)
  4. Check that the RockPro64 is plugged in
  5. Check that the RockPro64 has a valid bootloader installed in the appropriate media

I received my RockPro64 in the mail yesterday, and successfully used this process today.

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