INT 68 - APPC/PC - CONNECTION CONTROL - TEST
        AH = 02h subfn 1200h
        DS:DX -> control block
Return: control block updated
SeeAlso: 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)

.