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        Device busy loop (INT 15h, 90h)

        Entry:
          AH = 90h
          AL = Type code
                 00h: disk
                 01h: diskette
                 02h: keyboard
                 80h: network
                       ES:BX = NCB
                 FCh: disk reset
                 FDh: diskette motor start
                 FEh: printer
        Return:
          CF set if wait time satisfied
        Note: Type codes are allocated as follows:
              00-7F non-reentrant devices; OS must arbitrate access
              80-BF reentrant devices; ES:BX points to a unique control
                    block
              C0-FF wait-only calls, no complementary INT 15h, 91h call