INT 68 - APPC/PC
        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)