INT 68 - APPC/PC - TP STARTED
        AH = 03h subfn 2400h
        DS:DX -> control block (see below)
Return: control block updated

Format of control block:
Offset  Size    Description
 00h 12 BYTEs   reserved
 0Ch    WORD    2400h (verb "TP Started")
 0Eh  6 BYTEs   00h
 14h    DWORD   (big-endian) return code (see AH=01h/SF=1B00h)
 18h    WORD    00h
 1Ah  8 BYTEs   (big-endian) logical unit ID
 22h  8 BYTEs   (big-endian) TP ID

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