User's Manual

Appendix A
Using the Wiegand Interface
90
IDentity 4100 User Guide
A Wiegand frame consists of a string of bits transmitted in the Wiegand
format. Typically, this is 26 bits (including two parity bits). Following the
transmission of a Wiegand frame, a hold-off time (Thold) is asserted where
the Wiegand interface will not transmit. This mechanism is used to separate
adjacent Wiegand frames.
The unit, by default, outputs a 26-bit Wiegand frame (24 data bits , 2 parity
bits). Data lengths of up-to 128 bits can be accommodated. The current
default values for the Wiegand are as follows:
Parameter Value
TPW Pulse Width Time
50 µs
TPI Pulse Interval Time
2000 µs
Inter Frame Message Delay Time 250 ms
Data bits 24
Parity Standard
Bit format MSB first
For more information, refer to the AC-01 Wiegand Specification: “Access
Control Standard Protocol For The 26-Bit Wiegand Reader Interface”.
A.3. Wiegand Applications
Many access control panels incorporate a Wiegand Interface, and in many
applications a host reader will communicate with an access control panel
via the Wiegand Interface. Many Wiegand-enabled panels are configured to
receive Facility Code information and Serial Number information in Wiegand
format.
In an RFID-based access control system, the Facility Code and Serial
Number may be embedded into a data string known as a Translated ID. In
some applications, an actual tag ID may be mapped to a Translated ID via
some form of look-up table.
This ID4100 Wiegand application primarily uses secure tags for
authentication. The reader will read such tags and derive a Translated ID
from the tag. This Translated ID is then sent to the Wiegand Interface
Module (WIM) for transmission over a Wiegand Interface to a Wiegand
panel. However, a translation table facility is incorporated for managing
standard legacy tags.