Installing a USB Serial Adapter on Mac OS X

The easiest way to go about installing our Plugable USB to Serial adapter is by starting with the device.

  • If you want to verify that the adapter and the driver were installed properly click here

Connect the device to the Mac. Once connected click on the Apple icon and on ‘About This Mac’

Click on ‘More Info…’

Click on ‘USB’ on the left and on the ‘USB-Serial Controller D’
If all is well you should be seeing something like this:

Time to get the driver! Fire up Safari and browse to and scroll down to Mac.
Click on the ‘PL2303 MacOSX10.6 dmg’, the Safari Downloads window should come up:

Double click on the md_PL23-3_MacOSX10

Now double click on the PL2303_1.4.0.dmg to mount the image

Now double click on the PL2303_1.4.0 to start the installation

Once the installer comes up click ‘Continue’ to proceed.

Then ‘Select a Destination’ click on your desired drive and click ‘Continue’ to move forward

Now just click ‘Install’ to continue.

You may be asked of your username and password – enter them and click ‘OK’

You’ll get a warning about restarting the computer after the installation is complete. This is normal, click ‘Continue Installation‘.

Installing should start (takes a couple of minutes to complete)

When it’s done you should see this:

Click on ‘Restart’ to reboot the Mac.

 After you restart, check that everything has installed OK.
On the Mac there are two methods to determine this:

Method 1:
Click on ‘Applications’

Click on ‘Utilities’

Click on ‘Terminal’

kextstat | grep prolific
ioreg -c IOSerialBSDClient | grep usb
Your results should be very close to this:

Method 2:
Click on ‘System Preferences’

Click on ‘Network’

Now click on the ‘+’ sign on the bottom left, and then on the ‘Select the interface and enter a name for the new Service’ click on ‘Interface’ – you should be seeing the ‘USB-Serial Controller D’ there.

This will create a “Network” interface for a modem or serial port. Because it’s a serial port, it’ll say “Not Configured” and that’s normal:

From the “Advanced” button you can change default settings (usually not needed). And this won’t change the “Not Configured” message – that’s still ok.

Now finally, you need an application which will talk to the serial port. On Mac, the file which maps to the port is /dev/cu.usbserial. If you have a null modem cable and a terminal program on the other side, the Mac actually has a built-in terminal program called “screen” that you can use to test the connection.

Once that is up and connected (and if the serial ports are set to the same baud rate and paramters), you can type on either side and see the characters come across.


USB Serial on the Mac is a real melding of the very new and very old. If you have any trouble, just visit to see existing FAQs for Plugable’s USB Serial adapter.

Where to Buy

[amtap amazon:asin=B00425S1H8]

99 thoughts on “Installing a USB Serial Adapter on Mac OS X”

    1. Hi Dev,

      Thanks for asking. The USB to serial cable does work with Mac OS X V10.7. You’ll be able to use this same procedure to install it.


    2. Just for the records, i could successfully install the driver and use the USB-Serial adapter on Mac OS v10.8.2 (Mountain Lion). The only difference from the tutorial is that i had to alter GateKeeper configurations so a ‘non-signed’ driver could be installed. Before doing that change, Mac OS refused to run the driver installer because it wasnt from Apple nor from a certified developer. After changing that setting, installation went just fine and the adapter works nice !

    1. Hi Reinhard,

      Once you have the driver installed, the device will show up in the network dialog of system preferences. From there you just select the USB to Serial device, click the advanced button and select “null modem” as vendor. You’ll then be given options for baud rate.

      Hope that helps!

      Plugable Technologies

  1. hello . . .

    Thanks for the great write-up. Unfortunately, I hurredly installed the Mac OsX 10.6 driver, and it wouldn’t work, then I realized that I have OsX 10.5. Successfully downloaded it, but then get the error message ‘cannot install, newer version already installed’. I have spent the last hour trying to figure out how to uninstall the earlier version.

    Any help you can offer would be greatly appreciated.

  2. I’m bumping into a problem. Using the terminal I keep getting:

    $ cu -s 9600 /dev/cu.usbserial
    cu: /dev/cu.usbserial: System not found
    $ cu /dev/cu.usbserial
    cu: /dev/cu.usbserial: System not found

    I’ve uninstalled and reinstalled the drivers. I’m not sure what I’m missing.

  3. Hi Brad – Thanks for commenting with your problem. If /dev/cu.usbserial isn’t there, then something is going wrong. We see this happen on some Mac systems. Usually a unload/reload of the kext (driver) will work. And if not, there is an open source driver which seems to work as a last resort. Here’s a longish thread with some great historical info:

    If you can’t get to a good spot, please just contact us at and we’ll help however we can. Thanks!

  4. Hi Bernie,

    Just want to thank you for this great article. It just saved me a few hours of painful internet search for the Profilic MacOSX drivers and the installation steps. With your article, I’ve got it working like a charm.


  5. Hey GREAT write up. Thanks so much for this! Working on 10.7.4. Very happy that I don’t need my windows side anymore.

  6. If I install this on my MAC Pro (Lion) will it be available to work with an application in Windows XP via Parallels Desktop?

    1. Hi Stephen-

      Hopefully you’ve already found an answer to this, and the real answer here is to ask paralells whether your version supports mapping a usb device to your VM. From my experience Parallels handles passing a USB device to a VM fine with the exception of network interfaces, which it only knows how to share via a virtual interface.

      Hope this helps, sorry for the delayed response!

  7. Great article, work straight away,

    question about screen /dev/cu.useserial
    after run the commend serial output works fine, but I can not roll back to read previous text when the screen output reach the max raw of the terminal.

    is there an commend I can set to roll back 9999 line?

    1. Hi Sam, we’re glad to hear you found our article helpful!

      Getting scrolling in screen working is a little different depending on which version of osX you’re running and requires editing screenrc, unfortunately not a single command for this that I know of.

      Here is the best thread I’ve found on enabling screen scrollback (and more):

      Here’s another thread from stack overflow that talks about some options to enable scrollback in screen:

      A lot of people also prefer alternative terminals like Zterm, iTerm 2, etc. Several are mentioned in the stack overflow thread.

  8. Bernie – Fantastic description for a complete computer biff like me!

    Thanks – Garmin Foretrex 101 now running like a treat on my Mac….

    Good job…

  9. Hello,

    I got it working but I can not type anything into the windos, I have triied CU and Secure CRT and I see the devices booring up but it seems like my keystrokes don’t make it to the terminal.

    Thank you!

    1. Hi Maikel-

      We’re happy to try and help with this, however we’ll need a little further description of what you’re trying to accomplish.
      For the record and benefit of anyone else browsing the thread if you’d like assistance with our usb-serial adapter, we’re much better able to help if you explain what you’re trying to connect to, including details like the model number, and what steps you’ve been able to complete successfully.

  10. Hi

    I will be moving from PC to Mac, but will need to run a Windows application that uses a serial port, using boot camp. Would I be right in thinking I would need to install this adapter under Windows using a Windows driver?


  11. This modem only worked for me after I attached a Null Modem adapter to it – is this normal?

    I was hoping that selecting “Null Modem” under Preferences–>Network–>USB Serial Controller D–>Advanced would do the same in software – yes?

    1. Hi Scooby-

      I’m a little unclear on what you’re trying to connect to, but I definitely consider it normal behavior that you’d have to connect something to the adapter before being able to access it.

      Sorry if I’m misunderstanding your question, please feel free to clarify :-)

    2. A null modem cable acually switches the TX and RX wires in the cable. This is almost never done in software as far as i know.

  12. Trying to set up an Epson receipt printer with the adapter. I followed all instructions and in the network panel, when I click connect to the modem it says it cannot connect. Any suggestions?

    1. Hi Tyler-

      Thanks for posting with your findings!

      It sounds like this will be some sort of connection/device specific setting. If you’re able to post with some further details about the printer you’re connecting to such as the model number and possibly a link to a manual for the device we’ll do our best to help.

      Best wishes-

      Jeff Everett
      MCITP Enterprise Support Tech
      Plugable Technologies

  13. Hi,

    Loaded it all up fine, however my main purpose was that so I can telnet to devices on the serial port.
    My question is running the telnet what would I put after the telnet command to identify the port,

    at the moment I have

    unknown-00-26-08-f5-af-f4:~ chrismccann$ kextstat | grep prolific
    85 0 0×58412000 0×8000 0×7000 com.prolific.driver.PL2303 (2.0.0)
    unknown-00-26-08-f5-af-f4:~ chrismccann$ ioreg -c IOSerialBSDClient | grep usb
    | | | “IOTTYBaseName” = “usbserial”
    | | | “IOCalloutDevice” = “/dev/cu.usbserial”
    | | | “IODialinDevice” = “/dev/tty.usbserial”
    | | | “IOTTYDevice” = “usbserial”

    typically telnet com1 or an IP is put in, but for this device what would I use.

    many thanks,


  14. I’m trying to connect a USB-serial adapter in order to sync my old Pal IIIc to the Palm Desktop on my MacPro 10.6.8. Obviously the Palm is ancient but I need to have that data within my Mac as I want to phase out my PC.
    Anyway, I only get to the initial screen “establishing a connection” but then…nothing.

    Have any ideas?

    1. Hi Pierre-

      Did you successfully install the prolific driver before trying to connect to your palm? Was the USB Serial device added to your network connections as shown in our post?

      If so, feel free to drop us a line at, otherwise you’ll need to go through the steps in this post to install the driver.

      We’ll need to know more about which parts of the process you’ve been able to complete to be more helpful.

      Best wishes-


  15. this is wonderful, i’m new to the macbook pro, and need to make a cisco console connection. I do have a question, I’m struggling to find “screen”, to display my console session (with a network switch).
    Do i need to download software? I’m not sure what is the best method to configure my switches and routers.

    thanks in advance!

  16. hey, i got it! but, i’ve seemed to have hosed up the session (i quit). stating something about could not find a PTY session.

    man, so close!

    1. Hi Waudlob-

      Thanks for letting us know the tutorial helped on getting the initial connection going! If you’re having issues with device specific connection settings, checking with Cisco or whoever makes the device can be helpful- sorry I’m not sure specifically how to respond to the can’t find PTY session.

      Perhaps some of the resources here can be useful:

      I hope this helps!

      Best wishes-


  17. I wonder if anybody knows if there is any issues with the commonly available usb to serial cables that are so commonly purchased unwittingly that are a clone of the official pl2303.

    Prolific seem to be deliberately isolating compatibility against these devices in the newest Windows drivers, and wondered if thats the same with the mac drivers. Its just not worth wasting time putting in drivers to have to fight them out again when prolific deliberately make them to not work.

    Bah humbug @ prolific, not fair to cause issues for consumers when they should target the clone chip manufacturers directly!

    1. Hi Denis-

      Thanks for posting with your question. Indeed we can confirm that on Windows, there is code to check and prevent the Prolific driver from working with a counterfeit chip.

      As far as we know the check is only built into the Windows driver, we’re not certain if this is the same for OS X. Sorry we can’t provide more info here- I’d try and test on a lab mac but we don’t have any of the counterfeit cables lying around, only ours, the ones we know work ;-)

      If you have one of the counterfeit cables and find that these instructions don’t work, please post back for the benefit of all.

      Again, thanks for posting with your question.

      Best wishes-


  18. I use this adapter with my MBA running OS X 10.8.2. My only problem is my Mac crashes after disconnecting the adapter from the USB port. Has anyone run into this issue?

    Thanks in advance for any assistance.

    1. Mine crashes as well after unplugging the adapter from my MacBook Pro running OS X 10.8.2… starting to get very annoyed. :(

      1. Hi Frustrated-

        The short answer here is that you’ll need to make sure you’re properly terminating any applications or connections using the USB serial device to avoid this issue.

        We’ve actually seen this across platforms (Windows as well) and are communicating the issue back to Prolific, however in the meantime carefully exiting out of applications and killing processes where needed is your best workaround in the meantime.

        Here’s a more detailed explanation as to why:

        Best wishes-

        Jeff Everett
        MCITP Enterprise Support Tech
        Plugable Technologies

  19. My question is this… I can get terminal to see the device, and I can get screen to work and give me output, but all I get is gibberish instead of the data I should be seeing. I am using a USB to ttl adapter hooked into an ECD meter ( I admit, I am not a computer guru, but I’m at an impasse…

    1. Fazed, I would l look baud rate you are using for your device. I just had a similar issue connecting to an APC UPS management interface. if you are using screen try this command: screen /dev/cu.usbserial (Baud Rate). The baud rate is standard 9600 but you can change it by typing in the baud rate you wanna use i.e. 2400.


  20. After following these directions, and the install of the PL2303_1.4.0 appearing to be successful, I do not see the USB serial monitor option anywhere. Whether I look on system preferences under network or in terminal.

    In system preferences/netowrk, when I attempt to add a something, there is no USB option as indicated on this page.

    In Terminal, all I see is

    /dev/tty.Bluetooth-Modem /dev/tty.usbmodemfa141

    I believe the usb/tty.usbmodemfa141 is the Arduino USB driver I previously installed. But I never see a USBserial device or driver.

    I have an Xbee module and Xbee adaptor connected to the computer via a USB cable.

    This is on a Macbook Pro running 10.6.8

    also using CoolTerm I never see the USBserial option, only the USBmodem141 option.

    thans very much for any help, I’ve been struggling with connecting to these Xbee modules for a few weeks now.

    1. Hi Jordan (and any others who might be reading this)-

      One reason our instructions would not work is if you have purchased an FTDI chipset based USB Serial Device. Another common reason for the symptoms you describe would be trying to add the USB Serial Device to network connections when the cable isn’t connected to the system. If the Prolific Driver installer works without an error, then the commands below should return values similar to those listed above when run with the adapter connected:

      kextstat | grep prolific
      ioreg -c IOSerialBSDClient | grep usb

      If you are not seeing the expected output from these commands, please verify that your adapter matches the 3rd photo in our post, showing the entry in system profile:

      If your adapter does not match this entry, our instructions unfortunately will not be relevant for your adapter.

      If these instructions don’t work, please email with your Amazon order ID for further support.

      Best wishes-


  21. Hi.

    I’m trying to use a PL2303 USB-to-Serial cable with my Olimex SAM7-P256 board.
    I have the Prolific driver installed, and the device is recognized and appears as /dev/cu.usbserial
    The board has a standard RS232 port.

    It seems that no matter what I do, I get ‘gibberish’ characters. I’ve calculated the baudrate several times, it should be close to 9600 baud (9595) on the microcontroller.
    On my PowerMac G5, I tried using the network control panel to change the baud-rate, but no matter which rate I select, there is no change in the gibberish characters.
    The characters *only* changes when I change the baudrate on my microcontroller board, not on the computer.

    I also tried using cu –parity=none -s 9600 -l /dev/cu.usbserial dir
    -But I still don’t see the characters I’m sending from the microcontroller.

    Which end really controls the baud-rate, the one at the RS232 plug end or the one at the USB-plug end ?

    Any hints ?

    1. Neither end “controls”; they both have to match. Probably, either your baud rates don’t match (this is characterized by characters appearing on the interface “jerkily”–some stuff is recognized as characters, other stuff isn’t), or your bit count isn’t valid (some characters are readable, some aren’t). Parity generally manifests as most characters not coming through, or true gibberish, if the sender is delivering parity but the receiver isn’t receiving it.

  22. Good day,

    I’m trying to make my mac mini running 10.6.8 to communicate with my UPS, a Liebert PSA ITON 600. I followed all the instructions and I was able to install the driver and even got similar results after typing;

    kextstat | grep prolific
    ioreg -c IOSerialBSDClient | grep usb

    However, the software that came with the UPS still can’t detect any COM port in my mac mini.
    Any ideas?


  23. I am sure I can’t help you, because I gave up on my microcontroller communication, but I’d like to tell you what I would try (if you haven’t tried it already):
    1: Try unplugging your USB-to-Serial adapter.
    2: Open the terminal, type (without the $):
    $ ls /dev | grep usbserial
    3: You should see nothing after the above line, now plug in your USB-to-Serial adapter, then type…
    $ ls /dev | grep usbserial
    …You should see ‘cu.usbserial’ and ‘tty.usbserial’.
    If you see those two device names, I believe you should contact the manufacturer of the UPS.
    If you do not see the two device names, your USB-to-Serial adapter might be defective. Try verifying on a friends computer.

    OK, let’s assume you see the two device names.
    Open your “System Preferences”, then click your “USB-Serial Controller D” (or whatever it’s called), click the [-] button in the bottom of the panel (to remove it!), click “Apply” and quit System Preferences.

    Try your UPS software again and see if it works now.

  24. Oh, one more thing… Your UPS software might be programmed to recognize certain USB VendorID/ProductIDs. If you’re out of luck, they haven’t heard of the PL2303 chipset.
    If you’re lucky, they have made their software so it can recognize a generic serial port (and if you are *very* lucky, the software can be extended by editing the info.plist inside the application, so you can add a VendorID and ProductID yourself).

  25. Ei I typed the command and I was able to see ‘cu.usbserial’ and ‘tty.usbserial’ but my mac mini still won’t detect the UPS.. I guess I’m out of luck.. haha


  26. You’ve come a long way already. It seems your USB-to-Serial adapter is working.

    Did you also try removing the interface in the System Preferences ?
    Why would you want to do that ?
    Answer: Because exactly this might conflict with the UPS software.
    If it still doesn’t work, add it back in, also try configuring the baudrate to 9600 baud.
    Another thing: Try asking the UPS vendor if the name of the serial port is important.

    You verify that your USB-to-Serial adapter works by connecting either a modem or another computer via a null-modem cable (eg. a cable where only GND is connected and Rx is connected to Tx and Tx is connected to Rx; that’s all that’s necessary). Then open a terminal window on your Mac OS X machine and type
    $ cat /dev/cu.usbserial
    If you’ve connected another Mac OS X machine with another USB-to-Serial adapter, you can type…
    $ echo “Hello” >> /dev/cu.usbserial
    …Then the text should appear in the ‘cat’ window.
    You could also run for a ‘terminal program’ (I think PuTTY will work) on a PC and configure it to 9600 baud, 8N1.
    …Or if you have an easier way, just use that; eg. if you have an old 9600 baud Hayes modem, it would be fine for such tests. -Hmm… I actually have an old Hayes modem here, I could go and see if it works with my adapter. =)

    Also try and look in your manual for the UPS and read what it says about compatibility on the RS232 port. The vendor might have the manual available as a PDF download.

    I just searched the Web and it seems I’ve found their site. Try this page:
    -There are 3 interesting links:
    Product Information, Support and Service, “Customer Issues Department” and “Request technical assistance on product(s) already in use”. Perhaps the first one or the last one is most relevant.

    I’m not sure I can come up with other ideas, but perhaps someone else reading this might have a few suggestions.

  27. Thanks so much for all your input.. I’ve tried everything.. The interface wasn’t in the System Preferences to begin with so I added it and used different configurations, I also assigned the baudrate to 9600 baud, but still won’t detect… there is an ‘Auto-search for UPS’ feature in the software of the UPS and this shows up in the terminal:

    “Broadcast Message from localadmin@———-.local
    (no tty) at 23:21 EST…

    UPS Monitoring Software Message: Communication Lost: check connection and port
    setting. ”

    It can’t detect the tty… So i guess the UPS doesn’t support the adapter?

  28. I think there’s no problem with the UPS hardware. RS232 is RS232; it’s the same all over the World with all devices; fortunately it’s not messed up like most other standards. ;)
    -But the problem is with the software. Having written software for a PL2303 device myself, I know that there are a few things to do, to write the software properly.
    One thing *not* to do when writing software, is to use ‘/dev/somename’, because this changes like the weather; different device, different name.
    There might be one more thing left to try… If you right-click on your software application, you’ll see the “Show Package Contents” in the contextual menu. Choose this menu item. You’ll now see a folder called “Contents”, open it. In this folder, there might be more than one interesting file. You’ll have to do a bit of hunting yourself, but one thing I can suggest, is that you try dragging “Info.plist” onto your TextEdit application and look at the contents. Try and see if you can find a name of a serial port in there.
    If there’s nothing interesting in that file, try looking inside the “Resources” folder. files ending in .plist are usually the places where the developer would store such things, which could be tweaked or changed without re-compiling the application.

    From the terminal, you can also trying CD’ing to the application’s Contents folder and do a…
    $ grep -R -i “serial” *
    if nothnig found, try “tty” instead of serial. Still nothing ? -try “rs232″ or “uart” or “usart”.

    (Just a thought: I find it a bit weird, if the UPS vendor writes sofware to communicate with the UPS via RS232 and the same vendor does not mention anything at all about compatibility or how to actually connect the UPS in the manual – because why then use several months/years on writing the software? -But I guess some companies want to be strange.)

  29. I cannot get my iogear usb to serial adapter to work on my new Macbook Pro. So far I am stuck using it in Windows (Parallels) but would like to have it locally as well…I have downloaded the “GUC232A-Intel.dmg” file from their site..I go to system information->hardware->usb and see “USB-Serial Controller D”…when I launch SecureCRT or network..i only get “/dev/cu.Bluetooth-Modem” as my

    1. I followed the instructions, and got the driver to show in system report, but never in the network control panel. ZTerm worked, showing me that the driver works (and helped as a step), but minicom is the best app for the job- easy to configure, and remotely accessible with terminal. Great site- thanks for the help!

    1. Hi Varera – could you say what version of Prolific driver you have installed? Prolific has been making some updates (mostly targeted at 10.9), so there are a number of versions in the field right now. We’d like to find if one has a problem. If you can email also, we can start a support thread on it. Thanks!

      1. I reported the same problem a few months ago that Varera is having. I check periodically for updated drivers but I’m running the latest and still have the same problem. The only way to avoid crashes is to shutdown my Mac first, then unplug the adapter. Just closing the lid and unplugging still causes the Mac to crash.

        I would be interested in any updates on this issues.


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