You need a “Serial Debugging Tool”. In this guide we will use a “USB to TTL Converter”.


Follow these steps to make the correct connections:

1) Connect the Tool Pin to the GPIOs, and check the Tx/Rx Pin once more to ensure that you have amde correct connections:

  • Tool Pin GND: <---> Pin17 of VIM’s GPIO
  • Tool Pin TXD: <---> Pin18 of VIM’s GPIO(Linux_Rx)
  • Tool Pin RXD: <---> Pin19 of VIM’s GPIO(Linux_Tx)
  • Tool Pin VCC: <---> Pin20 of VIM’s GPIO

2) Insert the USB-end into your PC.

The connections should look like this:

Image of SerialConnections3Pin

Another photo for more details(VCC Pin is not necessary):

Image of SerialConnections

Setup kermit Protocol(c-kermit)

Install c-kermit:

$ sudo apt-get install ckermit

Add Access Permission:

$ sudo usermod -a -G dialout $(whoami)

Add the following contents into ~/.kermrc to finsh the setup:

Use nano,$ nano ~/.kermrc to create a new .kermrc file. Then copy-paste the contents below.

set line /dev/ttyUSB0
set speed 115200
set carrier-watch off
set handshake none
set flow-control none
set file tpye bin
set file name lit
set rec pack 1000
set send pack 1000
set window 5

After you’re done copy-pasting, save and exit nano.

Run command kermit to launch C-kermit

Ensure that you have made the correct connections. If everyting went well,you’ll see the following:

Connecting to /dev/ttyUSB0, speed 115200
Escape character: Ctrl-\ (ASCII 28, FS): enabled
Type the escape character followed by C to get back,
or followed by ? to see other options.


  1. If the treminal output contains this line, you might need to check the previous step Add Access Permission.

    /dev/ttyUSB0:Permission denied
  2. To access U-boot, leave your USB-Serial-Debug tool connected, then press the reset button on your device should see some print-out on your terminal, and then you’ll have access to U-boot.

3.If your terminal prints these

?SET SPEED has no effect without prior SET LINE
Sorry, you must SET LINE or SET HOST first

This is the wrong device to choose.Confirm your ttyUSB device number in the /dev directory and then modify .kermrc file