How can I use MC1489?
The RS-232 specification, and I'm taking this from memory so I'm obviously open to correction, provides these partial details:

MARK: \$-15\:\text{V}\le V \le -3\:\text{V}\$
SPACE: \$+3\:\text{V}\le V \le +15\:\text{V}\$
UNSPECIFIED: \$-3\:\text{V}\le V \le +3\:\text{V}\$
Receiver must tolerate: \$-25\:\text{V}\le V \le +25\:\text{V}\$
Receiver impedance: \$3\:\text{k}\Omega\le Z_\text{IN} \le 7\:\text{k}\Omega\$

The following schematic is for a single receive function.



simulate this circuit &ndash; Schematic created using CircuitLab
I added the diode in order to protect the base of \$Q_1\$ from MARK voltages, which is what the RS-232 line typically idles at. (For older RS-232 drivers, you'd routinely see \$-12\:\text{V}\$ or \$-15\:\text{V}\$. Newer ones may be much less, now, and not quite as much of a threat to a BJT. But it is better to be safer, than sorry.)