Common serial port names are /dev/ttyS0, /dev/ttyS1, etc. Thenaround the year 2000 came the USB bus with names like /dev/ttyUSB0 and/dev/ttyACM1 (for the ACM modem on the USB bus). Multiport serialcard used somewhat differnt names (depending on the brand) such as/dev/ttyE5.
- Apart from updating your PCI Drivers, installing a Driver Update Tool gives: Up to 3 times faster internet connection and download speeds; Better PC performance for games and audio applications; Smooth-running of all your PC devices such as printers, scanners etc. Better all-round performance of your PC due to automatic driver updates which will.
- A library of over 250,000 device drivers, firmware, BIOS and utilities for Windows.
Download source files - 10.4 Kb; Introduction. This tutorial will attempt to describe how to write a simple device driver for Windows NT. There are various resources and tutorials on the internet for writing device drivers, however, they are somewhat scarce as compared to writing a “hello world” GUI program for Windows.
Since DOS provided for 4 serial ports on the old ISA bus:COM1-COM4, or ttyS0-ttyS3 in Linux, most serial ports on the newer PCIbus used higher numbers such as ttyS4 or ttyS14 (prior to kernel2.6.13). But since most PCs only came with one or two serial ports,ttyS0 and possibly ttyS1 (for the second port) the PCI bus can now usettyS2 (kernel 2.6.15 on). All this permits one to have both ISAserial ports and PCI serial ports on the same PC with no nameconflicts. 0-1 (or 0-3) are reserved for the old ISA bus (or thenewer LPC bus) and 2-upward (or 4-upward or 14-upward) are used forPCI, where older schemes are shown in parentheses . It's not requiredto be this way but it often is.
If you're using udev (which puts only the device you have on yourcomputer into the /dev directory at boottime) then there's an easy wayto change the device names by editing files in /etc/udev/. Forexample, to change the name of what the kernel detects as ttyS3 towhat you want to name it: ttyS14, add a line similar to this to/etc/udev/udev.rules
On-board serial ports on motherboards which have both PCI and ISAslots are likely to still be ISA ports. Even for all-PCI-slotmotherboards, the serial ports are often not PCI. Instead, they areeither ISA, on an internal ISA bus or on a LPC bus which is intendedfor slow legacy I/O devices: serial/parallel ports and floppy drives.
Devices in Linux have major and minor numbers. The serial portttySx (x=0,1,2, etc.) is major number 4. You can see this (and theminor numbers too) by typing: 'ls -l ttyS*' in the /dev directory. Tofind the device names for various devices, see the 'devices' file inthe kernel documentation.
There formerly was a 'cua' name for each serial port and it behavedjust a little differently. For example, ttyS2 would correspond tocua2. It was mainly used for modems. The cua major number was 5 andminor numbers started at 64. You may still have the cua devices inyour /dev directory but they are now deprecated. For details seeModem-HOWTO, section: cua Device Obsolete.
For creating the old devices in the device directory see:
Dos/Windows use the COM name while the messages from the serial driveruse ttyS00, ttyS01, etc. Older serial drivers (2001 ?) used justtty00, tty01, etc.
The tables below shows some examples of serial device names. TheIO addresses are the default addresses for the old ISA bus (not forthe newer PCI and USB buses).
For more info see the usb subdirectory in the kernel documentationdirectory for files: usb-serial, acm, etc.
On some installations, two extra devices will be created,
/dev/modem for your modem and
/dev/mouse for amouse. Both of these are symbolic links to the appropriatedevice in
Historical note: Formerly (in the 1990s) the use of
/dev/modem (as a link to the modem's serial port) wasdiscouraged since lock files might not realize that it was really say
/dev/ttyS2. The newer lock file system doesn't fall intothis trap so it's now OK to use such links.
Inspect the connectors
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Inspecting the connectors may give some clues but is often notdefinitive. The serial connectors on the back side of a PC areusually DB connectors with male pins. 9-pin is the most common butsome are 25-pin (especially older PCs like 486s). There may be one9-pin (perhaps ttyS0 ??) and one 25-pin (perhaps ttyS1 ??). For two9-pin ones the top one might be ttyS0.
If you only have one serial port connector on the back of your PC,this may be easy. If you also have an internal modem, a program likewvdial may be able to tell you what port it's on (unless it's a PnPthat hasn't been enabled yet). A report from setserial (atboot-time or run by you from the command line) should help youidentify the non-modem ports.
If you have two serial ports it may be more difficult. You could haveonly one serial connector but actually have 2 ports, one of whichisn't used (but it's still there electronically). First check manuals(if any) for your computer. Look at the connectors for meaningfullabels. You might even want to take off the PC's cover and see ifthere are any meaningful labels on the card where the internal ribbonserial cables plug in. Labels (if any) are likely to say something like'serial 1', 'serial 2' or A, B. Which com port it actually is willdepend on jumper or PnP settings (sometimes shown in a BIOS setupmenu). But 1 or A are more likely to be ttyS0 with 2 or B ttyS1.
Send bytes to the port
Labels are not apt to be definitive so here's another method. Ifthe serial ports have been configured correctly per setserial, thenyou may send some bytes out a port and try to detect which connector(if any) they are coming out of. One way to send such a signal is tocopy a long text file to the port using a command like: cpmy_file_name /dev/ttyS1. A voltmeter connected to the DTR pin (seeSerial-HOWTO for Pinout) will display a positive voltage as soon asyou give the copy command.
The transmit pin should go from several volts negative to a voltagefluctuating around zero after you start sending the bytes. If it doesn't(but the DTR went positive) then you've got the right port but it'sblocked from sending. This may be due to a wrong IRQ, -clocal beingset, etc. The command '
stty -F /dev/ttyS1 -a' should showclocal (and not -clocal). If not, change it to clocal.
Another test is to jumper the transmit and receive pins (pins 2 and 3of either the 25-pin or 9-pin connector) of a test serial port. Thensend something to each port (from the PCs keyboard) and see if it getssent back. If it does it's likely the port with the jumper on it.Then remove the jumper and verify that nothing gets sent back. Notethat if 'echo' is set (per stty) then a jumper creates an infiniteloop. Bytes that pass thru the jumper go into the port and come rightback out of the other pin back to the jumper. Then they go back inand out again and again. Whatever you send to the port repeats itselfforever (until you interrupt it by removing the jumper, etc.). Thismay be a good way to test it as the repeating test messages halt whenthe jumper is removed.
As a jumper you could use a mini (or micro) jumper cable (sold in someelectronic parts stores) with mini alligator clips. A small scrap ofpaper may be used to prevent the mini clips from making electricalcontact where it shouldn't. Metal paper clips can sometimes be bentto use as jumpers. Whatever you use as a jumper take care not to bendor excessively scratch the pins. To receive something from a port,you can go to a virtual terminal (for example Alt-F2 and login) andtype something like 'cp /dev/ttyS2 /dev/tty'. Then at another virtualterminal you may send something to ttyS2 (or whatever) by 'echotest_message > /dev/ttyS2'. Then go back to the receive virtualterminal and look for the test_message. See Serial Electrical Test Equipment for more info.
Connect a device to the connector
Another way to try to identify a serial port is to connect somephysical serial device to it and see if it works. But a problem hereis that it might not work because it's not configured right. A serialmouse might get detected at boot-time if connected.
You may put a device, such as a serial mouse (use 1200 baud), on a portand then use minicom or picocom to communicate with that port. Thenby clicking on the mouse, or otherwise sending characters with thedevice, see if they get displayed. It not you may have told picocomthe wrong port (such as ttyS0 instead of ttyS1) so try again.
If the software shows that you have more serial ports than youhave connectors for (including an internal modem which counts as aserial port) then you may have a serial port that has no connector.Some motherboards come with a serial port with no cable or externalserial DB connector. Someone may build a PC from this and decide notto use this serial port. There may be a 'serial' connector and labelon the motherboard but no ribbon cable connects to its pins. To usethis port you must get a ribbon cable and connector. I've seendifferent wiring arrangements for such ribbon cables so beware.
If you don't use devfs (which automatically creates such devices) anddon't have a device 'file' that you need, you will have to create it.Use the
mknod command or with the MAKEDEV shell script.Example, suppose you needed to create
Drivers Micontrol Port Devices ListThe MAKEDEV script is easier to use.See the man page for it. For example, if you needed to make thedevice for
ttyS0you would just type:
If the above command doesn't work (and you are the root user), lookfor the MAKEDEV script in the /dev directory and run it.
This handles the devices creation and should set the correct permissions.For making multiport devices see Making multiport devices in the /dev directory.NextPreviousContents
Dec 21, 2020 • Filed to: USB Recovery • Proven solutions
Have you ever had difficulty connecting your devices to your computer using a Prolific USB to Serial adapter? If yes you are lucky to find this page, it will give you all the information need to fix an unresponsive Serial driver adapter. You may have noticed a yellow exclamation mark hovering over or beside the USB to Serial Driver when searching your Device Manager and if you have we can all agree that it signifies a prevailing problem.
Overview of the Error
If you are not able to connect your device to your PC using a USB to Serial adapter it may be that
- The USB driver is outdated
- The USB Driver is missing
- Or even a corrupted driver
While you can't be so sure what the exact problem is there are solutions you can adopt to fix the issue once and for all. Read on to find quick fixes to resolve the problem.
1# Fix Prolific USB to Serial Driver not Working
Solution: Roll your Prolific USB to Serial Driver back to an older version
Updating your drivers often work wonders for your system because it makes sure that it runs on the latest features that guarantee maximum functionality. Unfortunately updating your drivers can cause this kind of error especially if your latest update does not work too well with your hardware. Once you upgrade your PC to the latest Windows version your Prolific USB to Serial Driver also updates to the latest driver software and if the driver is not compatible with your Hardware issues may arise. To correct the error, you will have to download the driver again by following these steps.
- Right-click on your PC Start button and open Device Manager
- Double click LPT and COM ports then locate the Prolific USB to Serial Driver and right-click it so you can select Update Driver
- For driver software click My computer
- From My computer select 'Let me pick from a list of drivers available'
- Choose an older version from the list then click Next
- The driver you selected will be installed automatically
- Once it has been downloaded reconnect the driver to see if it works.
2# Fix Prolific USB to Serial Driver 'Coder 10'
Driver issues reveal themselves in so many ways or through messages such as
- This device will not start (Code 10)
- There is no driver installed in this device
- The driver was not successfully installed
A code 10 error may arise because the chip you are using is not an original one. If you are using a fake, the manufacturer has a way of disabling it due to copy write infringement and the copy write takes effect once you download a recent update. To protect your PC from getting this code, you will have to make sure that your Windows 10 never updates a driver without approval. Updates come in the form of 64 bit and 32-bit drivers. Below we will show you how to work your way around the problem.
Window 64 bit Fix
To fix Windows 64 bit OS including Prolific USB to Serial Adapter, follow through these steps.
- Download 'PL2303_64bit_Installer.exe and Save
- Remove every USB to Serial adapter from your PC and double click the 'PL2303_64bit_installer.exe
- Follow the prompt by plugging in one USB to Serial adapter the click on Continue
- Reboot your PC to get Windows up and running
If you have followed these process through and you still see the same error go to your device manager
- Open the control panel and navigate to Device Manager
- From your control panel navigate to the System category and click the Hardware tab
- Scroll to the LPT/COM port and double click Prolific USB to Serial Comm Port
- Click Drivers in the Properties section
- The Driver you choose should read '18.104.22.168 with an appropriate date attached
- If the date is wrong then it means the wrong driver was installed
- Unplug the Serial adapter and run the steps again to install the correct driver
For Windows 32-bit OS systems follow these steps
- You will have to download the 'PL-2303_Driver_Installer.exe and save from Microsoft download link
- Run the program and eradicate the driver if you can
- Run the installer once more to install a correct driver
To Troubleshoot for error if your device still does not work
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- Go to Control panel, enter System to access your Device Manager
- Scroll down to the LPT/ COM port then double click Prolific USB to Serial Comm Port
- Click Driver in the Windows Properties section
- The driver must be numbered as '22.214.171.124' and dates accordingly
If the driver was not installed, remove the Serial adapter then run 'PL2303_Driver_Installer.exe' again. Follow directions in Device Manager to download the correct driver
The three solutions listed in this article have proven to be quite helpful in fixing a Prolific USB to Serial driver not working on Windows 10. They may appear confusing at first but if you follow each step in detail you can resolve the issue.
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