ib technology
The RWD also operates as a standard Hitag 1 reader and the TTL level serial interface can be
used to read and write data for any of the Hitag 1 pages. Note that the READ and WRITE
PAGE commands are fully implemented as with the standard MicroRWD H1 version but the
READ and WRITE BLOCK commands have been removed for reasons of code optimisation.
In this manner the MicroRWD H1 “Wiegand” version is a highly flexible solution that will
report the H1 serial number as Wiegand outputs whenever a valid transponder enters the RF
field and can also be used to read/write any other memory area of the H1 transponder. OP3 is
also set high for two seconds after the Wiegand output to operate a buzzer and to allow for
separation of repeated data frames.
Wiegand Output Protocol
The Wiegand protocol (26 bit mode) itself is made up of a leading even parity bit (for b0 -
b11), 24 bits of data (from transponder data) and a trailing odd parity bit (for b12- b23). The
30 bit mode has the same format except 28 bits are used to form the data sequence.
For example:-
H1 serial number (Page 0) data (Hex):
04 60 22 12
Wiegand 26 bit sequence:- E (b0 --------- b11) (b12 -------- b23) O
E
1
( 0
4
6
0
2
2 ) O
0000 0100 0110 0000 0010 0010 1
Where E is EVEN parity bit for bit 0 to 11 and O is ODD parity bit for bits 12 to 23
The serial number of Hitag 1 transponders is unique and is set during manufacture, so the
Wiegand data will be different for each tag.
The complete Wiegand bit sequence is output whenever the tag is within the RWD’s antenna
field and the tag has been validated. This output is independent of the normal TTL serial
interface which responds to received commands and replies with the data as requested. The
physical Wiegand protocol is asynchronously transmitted as low going 50 mS pulses on the
appropriate DATA low or DATA high pins. These pulses are separated by 2mS periods. The
Wiegand sequence is output a single time whenever a valid tag enters the RF field for the first
time. The data frame is then followed by a two second delay (OP3 output pulsed high) before
normal operation continues (NO Wiegand output if selected length is ZERO).
Wiegand Protocol Timing Diagram
50mS pulse
5v
0v
DATA High
TTL level
2mS pulse intervals
DATA Low
DATA
5v
0v
1
0
1
0
2
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