This is an RS14 module which is connected to a shaft or car network on an Elevator. It has four connectors designed to interface to illuminated buttons.
In the case of the landing call buttons there would be a four wire network running down the shaft with power (30V) and data lines. The network cable loops past each of these modules in the LOP units (Landing Operating Panel) where two or more illuminated buttons will be plugged into it.
When a landing button is pressed the module communicates with the main controller to let it know, and then receives data back to turn on the LEDs in the button. Each of these modules has a set of address switches to indicate its position in the system.
I was expecting this to use a CAN bus network, but it appears to be a proprietary standard with Otis's own data transfer protocol. I was quite surprised to see that it didn't use a standard RS485 or other network driver chip, as they simplify the circuitry and are usually quite rugged.
At this point in time I haven't sussed out the communication circuitry, but I'll make a guess that the comparator is probably receiving a differential signal and the module may be using a discrete push-pull circuit to put data onto the network.
I'm wondering if the RSL (Remote Serial Link) system is just an early standard that Otis developed and have continued to use due to their core software being based around it.
As with many other things, the module has been cloned in many forms. You can get copies for around £10, although it should be noted that if the software they use is a bad clone then they could cause network reliability issues.
When I was trying to identify the chip based on the Otis part number I found many Chinese sellers offering the chip for sale. I'm not sure if it's the real thing or a clone.
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