Reader to Board communication 

There are two formats in which this communication works, Weigand and OSDP. Weigand has been around for a long time, it refers to the communication method between the reader and the door controller. It is a “protocol”. It is a one way communication method from the reader to the door controller. It was invented in the 70’s by John Weigand.  

OSDP (open supervised device protocol) is a more recent development. OSDP allows for communication between both the reader to the controller and the controller to the reader. It can detect reader issues as well as cards, i.e. has the reader been tampered with.