Hey evryOne!

How about wiegand protocol? Did some search with my
web archive engine and there is lot of info available out there;-) But
I could not understand how a MCU and RS232 can communicate over this
protocol? I mean that there are tow data lines representing '0' and
'1' in wiegand, where as normally dealing with RS232 we use MAX232
line driver's tow pins that are Rx, and TX for receiving and
transmitting respectively. Though there are extra tow Rx and Tx
available on line driver (MAX232) but still can't figure out how to
do that? And finally is it that worthy (fast) then direct UART or SPI?

Hey! Is there any thing that Intel guys have developed for
communication over a single line? heard from some one but don't kow
about that;-)


ali

"Ali" <abdulrazaq@gmail.com> wrote in message
news:1157795335.512170.81730@p79g2000cwp.googlegro ups.com...

Weigand is a primitive TTL level protocol that no one in their right mind
would use unless they needed to communicate with Weigand devices. These are
commonly used in the security and access control industries. A MAX232
would not normally play a part in a weigand interface. It would be as
superfluous as mammary glands on a male bovine.

Weigand is a slow protocol (500 baud), certainly not comparable to most UART
or SPI interfaces.

I believe that Intel has recently invented the 2CANbus, comprising
accoustically coupled FeSn communications diaphragms within cylindrical
resonating chambers, coupled by a single line. Be prepared for this to play
a major role in pre-pubescent espionage and counter-espionage simulations in
the near future.

Cheers,
Alf.

Alf Katz wrote:
However there are major problems with that bus, having to do with
the physical makeup of the line and its tensile strength. The bus
length is strictly limited, and must use line-of-sight. Bandwidth
is also a problem. Protocols for its use are nebulous.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>



--
Posted via a free Usenet account from http://www.teranews.com
Warning: Do not use Ultimate-Anonymity
They are worthless spamers that are running a scam.

Ali wrote:
The Wiegand output signals Data0 and Data1 are usually open-collector
and can tolerate a voltage up to 15V or more. You could use an RS-232
level-shifter, such as the MAX232 to get logic level signals your uC
could deal with, even though the Wiegand signals never go below 0V.
Your code would have to catch every negative spike on the Data0 and
Data1 lines and shift an appropriate bit ('0' or '1') into a virtual
shift register.
The easiest way to do this is to connect the level-shifted Data0 and
Data1 signals to two interrupt pins of your uC.

There are several Wiegand formats, differing in the number of bits,
type of parity checking etc. I think that only the 27 bit variant is
documented, all the longer ones being proprietary.

Try searching HID and Motorola sites for the exact format.

Hi Ali,

My limited understanding is as follow...

Early Wiegand ISO cards had 2 rows embedded in to a card.

Each row had a tiny strips of metal placed along the card..

One row was logic '1' and the other row was for '0'.

Like this


'0''s I I I I
'1''s I I I I I I


So the logic sequence from left to right would be 0110110110

So when you swiped the card accorss the reader this is the logic sequemce
that is picked up.

See page 3 of this web link
http://www.cdvamericas.com/PDF%20ENG...d%20signals%22


So typically a micro monitors signals on the '0' data line and the '1' data
line....

So You will need to use a micro or similar as a "bridge" to convert the
non-popular Wiegand to UART-RS232.


Typically the physically layer is "open-collector" / "open drain" with pull
ups....


Regards
Joseph Goldburg


"Ali" <abdulrazaq@gmail.com> wrote in message
news:1157795335.512170.81730@p79g2000cwp.googlegro ups.com...

Joe G (Home) wrote:

Thanks every body. Yes, things are quite clear now, for example MCU
might be listening on tow external interrupts for falling(DATA0) and
rising(DATA1) edges. Then it packs the data in either 26 or 44 format,
and finally pushing it to host (RS232, MCU etc..).

I have observed that weigand is widely used in access control systems
but really can't understand why weigand? As few folks in this thread
have also pointed that its not that fast so what is the key benefit of
weigand in access control systems?

Say i have a reader and MCU, reader will output the data in linear way
, right? so that does not make any difference if i use tow interrupts
or one to decode incoming signal because it will never overlap.
I might be wrong but do you people think that this approach (weigand)
in RFID readers can improve the performance?



ali

Ali wrote:
ordinary UART-talk, for example, the parties must agree on a given data
rate. Usually, that's no problem.
But if the data source is a hand-swiped card, the bit-rate off the card
can be anything. To pass that to a UART will require some buffering.
That added majorly to the cost, back in the 1970's.

David R Brooks wrote:


So the bottomline is not to use weigand if UART is way down in
communication link , right?


ali

You have to use Wiegand:

a) If you are making an access-control or time-attendance unit and will
not be making the readers yourself. Chances are you will find the
largest selection of card readers, keypads etc. with Wiegand outputs.
Having Wiegand inputs on your controller is thus a good idea.

b) If you want to make a card reader, keypad etc. for use by other
people's controller boards. Since most of them provide Wiegand inputs
(for reasons stated in a), your readers will connect easily to their
boards.

This closed loop is the reason why there are even fingerprint readers
with Wiegand outputs!

"Viktor" <vkesler@gmail.com> wrote in message
news:1158081078.097918.215770@b28g2000cwb.googlegr oups.com...
Is that still true? In my experience with cardreaders and access control
systems (in Europ, that is) most systems have an Omron interface as common
denominator, which has a data, clock and cls (Card Load Signal) signal.

Meindert

"Ali" <abdulrazaq@gmail.com> wrote in message
news:1158075033.811071.280660@d34g2000cwd.googlegr oups.com...
The bottomline is not to use Weigand unless you need to (i.e. the device
you're talking to uses Weigand), and if you need to, then use it regardless
of what else is in the comms chain. If you're asking this question, then
you probably would not use Weigand.

It would be real strange to use it as a general communications physical
layer, it's not an alternative to standard NRZ as used in UARTs. It would
be like travelling to work in a wheelchair instead of a car/train etc. It
could be done, but you wouldn't do it unless there was a darn good reason.

Cheers,
Alf

Alf Katz wrote:

Wao! that sounds more interesting ;-)

Meindert Sprang wrote:

I've seen more pigtailed card readers with Wiegand or Wiegand/magcard
outputs than magcard-only types.
We use iButtons for our controller boards. Since a lot of customers
wanted to keep existing RF cards (and readers), we developed a
Wiegand/iButton inteface so we could attach their existing readers to
our controller. We also have a magcard/iButton interface, but we've
never used that for anything other than actual magcard readers with TTL
outputs.

IMHO emulating magnetic cards in modern equipment is no better than
emulating Wiegand cards. It's just as unidirectional as Wiegand and
since magcard emulation usually adheres to the track2 format, you're
limited to something like 4 bits/character.

Viktor