Patent ID: 6988203

Claim:
An access control security system comprising: a) a control panel; b) a plurality of access control groups, each access control group interconnected to the control panel on an independent multi-wire data bus, each access control group comprising: an access interface unit comprising: data output means for transmitting data onto the data bus to the control panel, data input means for receiving data via the data bus from the control panel, processing means, interoperating with the data output means and the data input means, for operating data transfers over the data bus, the processing means adapted to generate a data message for transmission onto the data bus via the data output means, the data message comprising a Wiegand message field in accordance with the Wiegand protocol; wherein at least one of said access interface units is further adapted to implement an extended data field along with the Wiegand message field, and wherein the control panel is adapted to communicate with each access interface unit to determine if the access interface unit is capable of implementing the extended data field, and if the control panel determines that the access interface unit is not capable of implementing the extended data field, then the control panel communicates with that access interface unit in accordance with only the Wiegand protocol, and if the control panel determines that the access interface unit is capable of implementing the extended data field, then the control panel communicates with that access interface unit in accordance with the Wiegand protocol and the extended data field.