Something like an SN75477 interface driver chip would work. Basically it is an open collector transistor with some glue logic. If you want some isolation use an opto-isolator like a PS2801-1. It is an LED driving a phototransitor. Just connect the phototransitor outputs up like a standard open collector driver.
JIC, an open collector drive output is just a series resistor connected to a positive voltage on one end and the other end connected to the collector pin of the transistor. The emitter is connected to ground and your output signal is connected to the collector as well, sometimes through an isolation resistor.
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