Microsoft KB Archive/139293

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BUG: Locked Keyboard When SHIFT or CTRL Key Is Pressed

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Q139293

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The information in this article applies to:


 * Microsoft Win32 Device Driver Kit (DDK) Windows 95

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SYMPTOMS
The keyboard driver sample in the Windows 95 DDK as of November 1995 includes the DDL code for Kbd.drv which is intended to be substituted for the Keyboard.drv in System.ini. In other words, use "KEYBOARD.DRV=KBD.DRV" to test it. It is in the Keyb\Samples\DriverS subdirectory. Unfortunately, there is a bug in the sample code that, when made, locks up the operating system when SHIFT or CTRL keys are pressed.

CAUSE
There is an indirect call to Int16 in the file Toascii.asm. You can find it near the end of the file by searching for [LightsAddr]. The call requires AH to be set to 0x01 but the register is not loaded with any value.

RESOLUTION
Insert a line immediately before the line that places an indirect call to Int16 in the file Toascii.asm to load the register:

  MOV AH,1  ;bug fix

This had been tested successfully.

STATUS
Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.