USB to serial adapter

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This type of adapter allows you to add several serial (RS232) ports to your APF board, through the USB Host interface (available on DevFull, APF27Dev, APF51Dev and APF28Dev)

Tested materials

Warning Warning: Due to some bugs in the (uggly) ISP1761 driver, USB to serial adapters are currently not usable on the APF9328 !

The commercial adapters can be separated in 2 categories, because there are only 2 USB<->serial low cost chipmakers:

  • FTDI one
  • Prolific one (pl23xx)
Adapter Model Chip Status
APF9328 / APF27 / APF51 / APF28
Driver Comments
Trendnet TU-S9 pl2303 KO OK NT NT pl2303


 $ make linux-menuconfig
 Device Drivers  ---> 
     [*] USB support  --->
               *** USB port drivers ***
         <M>   USB Serial Converter support
             <M>   USB FTDI Single Port Serial Driver
             <M>   USB Prolific 2303 Single Port Serial Driver
 $ make linux && make

copy following drivers on your target or reflash your rootfs (for more infos, see this page)



  • be sure that your USB Host is running on your board: explanations are here
  • plug your USB adapter (here a Prolific one)
usb 1-1: full speed USB device using mxc-ehci and address 2
usb 1-1: configuration #1 chosen from 1 choice
usb 1-1: New USB device found, idVendor=067b, idProduct=2303
usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
usb 1-1: Product: USB-Serial Controller D
usb 1-1: Manufacturer: Prolific Technology Inc.
  • Load the module, for example if you have a Prolific based adapter:
# modprobe pl2303

usbcore: registered new interface driver usbserial
usbserial: USB Serial Driver core
usbserial: USB Serial support registered for pl2303
pl2303 1-1.1:1.0: pl2303 converter detected
usb 1-1.1: pl2303 converter now attached to ttyUSB0
usbcore: registered new interface driver pl2303
pl2303: Prolific PL2303 USB to serial adaptor driver
  • a new serial device will then appear under /dev/ttyUSBN (N starting at 0 and depending on the number of adapters detected).
Note Note: You can now use this new device like a standard Linux serial port


  • If your USB <-> Serial converter doesn't seem to work, run the dmesg command. You should read this thread if you see some disconnection data like this :
[ 2445.568000] usb 1-1.4: new full speed USB device using uhci_hcd and address 22
[ 2446.964000] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
[ 2446.964000] ftdi_sio 1-1.4:1.0: device disconnected