INT 78 - TARGA.DEV - SEND SCSI COMMAND AND DATA (PROGRAMMED I/O)
        AH = 12h
        DS:SI -> command bytes
        ES:BX -> data storage area
        CX = number of data bytes to transfer
Return: AH = SCSI status byte
        CF clear if successful
            AL = SCSI message byte
        CF set on error
            AL = error code (see AH=00h)
Note:   this command sends data internally one byte at a time

Format of SCSI Command:
Offset  Size    Description
 00h    BYTE    length of command
 01h    ???     command bytes