Int 68 Fn 02  - Appc/pc - Connection Control - Test                        [N]

   AH = 02h subfn 1200h
   DS:DX -> control block

Return: control block updated

See Also: AH=02h/SF=1300h

Format of control block:
Offset Size    Description
 00h 12 BYTEs  reserved
 0Ch   WORD    1200h (verb "Test" or "MC_Test")
 0Eh   BYTE    1 if MC_ (mapped conversation) form of verb
       0 if basic verb
 0Fh  5 BYTEs  reserved (0)
 14h   WORD    (big-endian) primary return code (see AH=02h/SF=0100h)
 16h   DWORD   (big-endian) error code (see AH=02h/SF=0100h)
 1Ah  8 BYTEs  (big-endian) TP_ID
 22h   DWORD   (big-endian) conversation ID
 26h   BYTE    (MC_Test only) test (0=posted, 1=request_to_send received)

       Note: error code has different interpretations for:
           0 posted data
           1 posted not data (primary return code = 0)
           1 bad TP_ID (primary return code = 1)