wiegand protocol

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

Reply to
Ali
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Yeah, how about it!

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.

Reply to
Alf Katz

... snip ...

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.
Reply to
CBFalconer

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

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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

Reply to
Joe G (Home)

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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

Reply to
Ali

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One great strength of Weigand is that it is speed-independent. With 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.

Reply to
David R Brooks

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

ali

Reply to
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!

Reply to
Viktor

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

Reply to
Meindert Sprang

Wrong, 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

Reply to
Alf Katz

etc. It

Wao! that sounds more interesting ;-)

Reply to
Ali

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

Reply to
Viktor

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