...that was actually what i was looking for. the connection is half-duplex and probably won´t be multi-drop...and i´d have a question, if i don´t bother: when using the max489 for a single connection, does it make sense to connect A&Y and B&Z? i found a circuit in the net doing this, and now i wonder if it is some safty thing or stuff...
If your communication is bi-directional and half-duplex, then you need to connect A/Y & B/Z. It is not a safety thing: it is the definition of a half-duplex connection. Half-duplex requires only two wires, but only allows communication in one direction at a time. The A/Y & B/Z connections are so that the transciever can both write and read the bus.
Note that something else needs to ensure that the two sides are not trying to write to the bus at the same time. That can be either a set of additional wires used for bus arbitration signaling between your sensor and your Arduino, or it could just be a set of agreed-upon conventions. E.g., Arduino asks for data, then turns the bus over within X ms so that the sensor can write the data back, including some implicit or explicit indication that the data packet is complete. Whether you have the Arduino set to idle as bus master or the sensor depends on synchronization between the Arduino and the sensor, and whether the data is read in a request-response model as above, or just streamed by the sensor.
It will also be easier if you can commit to either multi-drop or not right now, rather than saying "probably not multi-drop." It is more complicated to do bus arbitration and avoid multiple bus-writers in the half-duplex multi-drop case.
There is a lot one needs to know about your particular sensor and the data protocol in order to answer your real question, which is "how do I hook this up and make it work."