Int 15 Fn 2400  - System - Later Ps/2s - Disable A20 Gate                  [b]

   AX = 2400h

Return: CF clear if successful
       AH = 00h
   CF set on error
       AH = status
       01h keyboard controller is in secure mode
       86h function not supported

Note:  also supported by Qualitas 386MAX v6.01+

See Also: AX=2401h,AX=2402h,AX=2403h