I am trying to access a network device console from my mac using a Prolific Technology USB-serial adapter to the device's console. After installing the relevant driver, the adapter is correctly shown:

$ ioreg -p IOUSB -l
    +-o USB-Serial Controller@14200000  <class AppleUSBDevice, id 0x10000034a, registered, matched, active, busy 0 (101 ms), retain 11>
    |   {
    |     "sessionID" = 1402970206
    |     ...
    |     "bDeviceSubClass" = 0
    |     "bcdUSB" = 272
    |     "USB Product Name" = "USB-Serial Controller"
    |     "PortNum" = 2
    |     "non-removable" = "no"
    |     "IOCFPlugInTypes" = {"9dc7b780-9ec0-11d4-a54f-000a27052861"="IOUSBFamily.kext/Contents/PlugIns/IOUSBLib.bundle"}
    |     "bDeviceProtocol" = 0
    |     "IOUserClientClass" = "IOUSBDeviceUserClientV2"
    |     "IOPowerManagement" = {"DevicePowerState"=0,"CurrentPowerState"=3,"CapabilityFlags"=65536,"MaxPowerState"=4,"DriverPowerState"=3$
    |     "kUSBCurrentConfiguration" = 1
    |     "Device Speed" = 1
    |     "USB Vendor Name" = "Prolific Technology Inc."
    |     "idVendor" = 1659
    |     "IOGeneralInterest" = "IOCommand is not serializable"
    |     "IOClassNameOverride" = "IOUSBDevice"
    |   }

To access the console, I started screen from Terminal as per below:

$ screen /dev/tty.usbserial 9600

When I power on the connected network device, I can see the cursor bounces around randomly as if responding to the device console output, however no characters appear on Terminal at all. I know the USB-serial adapter is working fine, as using it on a Windows machine, I am able to access the same network device console without any issue. Any idea how to address this?

Thank you.

  • What information in ioreg lead you to /dev/tty.usbserial (and what is 9600 for)?
    – samus
    Nov 1, 2021 at 15:43
  • 1
    ioreg output showed that the usb-serial adapter was recognised by macOS. About those screen parameters, check this link.
    – Heelara
    Nov 3, 2021 at 11:12

1 Answer 1


Since I couldn't get this working on my mac after multiple days, I decided to try my luck with a Debian 9 VM running in VMware Fusion within this mac. As soon as I made the device available within Debian VM, it was automatically detected and an associated tty* device was created:

# lsusb
Bus 002 Device 002: ID 0e0f:000b VMware, Inc. 
Bus 001 Device 005: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port
$ ll /dev/ttyU*
crw-rw---- 1 root dialout 188, 0 Dec 29 14:30 /dev/ttyUSB0

Unlike /dev/tty.usbserial within macOS which was open for group others, device /dev/ttyUSB0 wasn't. So, I started screen with sudo:

$ sudo screen /dev/ttyUSB0 9600

And voila, it worked, as per the following screenshot! BIOS setup

I guess this is still a workaround. Checking the screen status (Ctrl-a + Ctrl-i (macos), Ctrl-a + i (Linux)), the latter had CD in brackets, implying signal CD was in effect: Port status

That is the only significant difference that I could spot. Hope this helps others.

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