Appc/pc

        Entry:
          AH = 04h
          DS:DX -> control block (see below)

        Format of control block:

        Offset  Size    Description
         00h 12 BYTEs   reserved
         0Ch    WORD    verb (action)
                        2500h TP_ENDED
                        2900h TP_VALID
         0Eh  6 BYTEs   0
         14h    DWORD   (high byte first) return code (see AH=01h)
         18h    WORD    0
         1Ah  8 BYTEs   (high byte first) TP_ID
         22h    DWORD -> CREATE_TP record (only if verb = 2900h)