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When the ULINK device is connected, the LED Power must be ON. After the ULINK startup period, the LED's COM and RUN flash for about 1 second. This verifies that the device is connected and is recognized by the PC.

Solve ULINK Communication Problems

If the ULINK device fails, right click on My Computer and select Properties to open the System Properties dialog.

Under Hardware - Device Manager... check the status of all connected USB devices.

Click on Universal Serial Bus controllers - Keil ULINK to open the Keil ULINK Properties dialog. This dialog page displays the status of the USB device.


Reinstall the ULINK USB Driver

If this driver does not work as shown above, reinstall the Keil ULINK Driver using the following steps.

  1. Login to your computer as an administrator. This is required to make registry changes on Windows 2000/XP.
  2. Delete all *.INF files containing USB\VID_c251.
    1. Use Start - Search - For Files or Folders. Specify *.INF as the file name, VID_C251 as the search text, and the base folder of your operating system as the search location (typically, this is C:\WINNT\ for Windows 2000 and XP computers).
    2. Start Search should present a list of INF files (like KeilUL.INF and and OEM4.INF). Delete these files.
    3. Windows 2000 and XP create precompiled setup information files that have the same name but with a *.PNF extension (like KeilUL.PNF and OEM4.PNF). You must delete these files, also.
  3. Delete KeilUL.SYS and KeilUL0.SYS from the C:\WINNT\SYSTEM32\DRIVERS or C:\WINNT\SYSTEM32\DRIVERS folder.
  4. On Windows 2000 and XP use RegEdt32 to remove all registry entries with USB Vid_c251.
    1. Run RegEdt32 (not RegEdit) from the start menu.
    3. Delete the folder with Vid_251. You may need to change access rights under Security - Permissions to do that.
  5. Reboot your computer.
  6. Update the Keil PK51 software.

Now the Keil ULINK Adapter drivers are completely uninstalled. If you plug in the Keil ULINK again the Windows computer shows a Detect New Hardware.  If this message is followed by the Found New Hardware Wizard dialog, select: 

  • Install Hardware Device Drivers - Search for a suitable driver for my device.
  • Locate Driver Files - Specify a location. Select the file KeilUL.INF for the Keil ULINK Adapter. This file is included in the Keil Development Tools download in the folder KEIL\SETUP\DRIVER\DRIVERS.
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