Paxton security keypad protocol

Hi.

I want to emulate a keypad for a Paxton security system with an arduino, so I can make a adaptor that allows me to use a industrial HMI screen (Mitsubishi E1101) as a keypad.
I already have modbus working between the display and another arduino, so I think I will use modbus for this aswell.
I've got this part under control.

The problem for me is the communication between the arduino and Paxton controller.
I have used my logic-analyzer to see what the keypad is sending when pressing the different keys.
at idle, both "DATA" wires are high at 5V, and when I press a key, the lines are pulled down to send a clock on one of the wires, and data on the other.

I have also tested the keypad without being connected to the controller, and it transmitt the exact same clock and data, so it seems to be a one-way transmission.

The image shows what happens when I press the different buttons (0-9,#,* and bell)
The clock is the exact same for each key.
I added the red lines when I tried decoding it, but it did not help me understand.

Does anybody recognize this protocol?
How feasable will it be to replicate this?