Data interfaces
35
Siemens Building Technologies
Fire Safety & Security Products 07.2008
13.2 Data Hold input
With the Wiegand and Magnetic Stripe interfaces, the Data Hold input (H) can be
used by the host to buffer one data message in the Reader until the host is ready
to read it. This enables the data lines from two Readers to be connected in parallel,
the host polling each in turn by releasing its Data Hold input, reading the data, then
asserting the Data Hold input again. The Reader will store the message until the
next card is read.
13.3 Wiegand
13.3.1 Connections
The pin connections for the Wiegand interface are as follows:
0V Ground
D0 Logic 0
D1 Logic 1
DA Data available
13.3.2 Electrical characteristics
The interface provides three outputs: logic zero data D0, logic one data D1 and
data available DA.
Data transfer is performed by pulsing the D0 line to indicate a logic zero and by
pulsing the D1 line to indicate a logic one. The pulses are active-low. The voltage
of the data lines is +5V or 0V.
The Data Available output DA is provided to tell the host system it must read a data
message from the Reader. If the Data Hold input see above is not active, DA be-
comes active 1ms before data is sent and is released 1ms after the data has been
sent. If the Data Hold input is active, DA becomes active but data is not sent until
Data Hold is released, DA remaining active until 1ms after the data has been sent.
When used in association with the Data Hold input see above, DA enables the data
lines from two Readers to be connected in parallel. The polarity of the DA output is
active-low.
To Next Page
Loading...
