A method that transfers a small amount of data using D0 and D1. Generally it is used as a method of communication between the reader and controller of an access control device.

When a 0 is sent the D0 wire is pulled to a low voltage while the D1 wire stays at a high voltage. When a 1 is sent the D1 wire is pulled to a low voltage while D0 stays at a high voltage.

[Example]

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