Int D4 Fn 23  - PC-mos/386 V5.01 - Change Terminal Driver                  [O]

   AH = 23h
   BX = task ID (FFFFh for current task)
   DS:SI -> entry point of the new Device Driver Terminal

Return: CF clear if successful
   CF set on error
       AX = error code (see INT 21/AH=59h)