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'[PIC] I2C Broadcast Question'
2004\10\25@081949 by Lucian Copat

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face
Hello to all readers !

I have a simple question for the more documented of you: I would like to
have more devices on a I2C bus and broadcast to a specific group of them.
The architecture will be one master/many slaves. Is it possible to assign
addresses to them so to be able to broadcast only to a specific address
range ? E.g.: to broadcast to 0101XXX0 where XXX would be all devices within
this range ?

Thank you in advance for your answers.

Lucian

____________________________________________

2004\10\25@083615 by Bob Axtell

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The problem is that all of the devices in that XXX range will apply an
ACK simultaneously. Won't work, sorry


--Bob.

Lucian Copat wrote:

{Quote hidden}

>_____________________________________________

2004\10\25@083858 by Bob Axtell

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On 2nd Thought. If you NEVER have any intention of ever READING a
particular device, it would
probably work just fine.

--Bob

Lucian Copat wrote:

{Quote hidden}

>_____________________________________________

2004\10\25@090325 by Lucian Copat

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Yes, you are right, I have to find another solution. Thank you very much for
answering !

Lucian

----- Original Message -----
From: "Bob Axtell" <spam_OUTengineerTakeThisOuTspamcotse.net>
To: "Microcontroller discussion list - Public." <.....piclistKILLspamspam@spam@mit.edu>
Sent: Monday, October 25, 2004 3:36 PM
Subject: Re: [PIC] I2C Broadcast Question


{Quote hidden}

within
> >this range ?
> >
> >Thank you in advance for your answers.
> >
> >Lucian
> >
> >_______________________________________________

2004\10\25@090440 by Alan B. Pearce

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>Is it possible to assign addresses to them so to be
>able to broadcast only to a specific address range ?
>E.g.: to broadcast to 0101XXX0 where XXX would be
>all devices within this range ?

No, the best you could do would be to issue a broadcast message, with an
indicator within the message that the slaves used to identify if they should
react to it.

However I believe you could what you want if you went to the CAN bus, but
this is just my belief from a short perusal of the spec, I have no actual
experience with it.

____________________________________________

2004\10\25@092550 by olin_piclist

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Lucian Copat wrote:
> I have a simple question for the more documented of you: I would like to
> have more devices on a I2C bus and broadcast to a specific group of
> them. The architecture will be one master/many slaves. Is it possible
> to assign addresses to them so to be able to broadcast only to a
> specific address range ?

Not if you want the address filtering to be done in software.  If you
implement the IIC slave in software, then you could add such address
filtering.  If you want to use the hardware, you would have to send a
general broadcast, then include some additional information in the packet so
that your devices know whether to respond or not.  I suppose you could set a
group of devices to the same address and again use additional information in
the packet so each of those devices knows what to do.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
____________________________________________

2004\10\25@093145 by olin_piclist

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Bob Axtell wrote:
> The problem is that all of the devices in that XXX range will apply an
> ACK simultaneously. Won't work, sorry

Multiple slaves replying with ACK is not in itself a problem.  After all,
that happens normally on a general call (broadcast).  It is only a problem
is some slaves might not always be there and you need to know.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
____________________________________________

2004\10\25@130704 by olin_piclist

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Olin Lathrop wrote:
> Lucian Copat wrote:
>> I have a simple question for the more documented of you: I would like
>> to have more devices on a I2C bus and broadcast to a specific group of
>> them. The architecture will be one master/many slaves. Is it possible
>> to assign addresses to them so to be able to broadcast only to a
>> specific address range ?
>
> Not if you want the address filtering to be done in software.

Oops, that should have read "in hardware".  Sorry.

*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
____________________________________________

2004\10\26@065948 by Peter L. Peres

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On Mon, 25 Oct 2004, Bob Axtell wrote:

> On 2nd Thought. If you NEVER have any intention of ever READING a particular
> device, it would
> probably work just fine.

Not sure about that. The ack puse could cause trouble. Also many devices
need a two-word addressing scheme. The master would never know if the
lights are on but there's nobody home at the other end.

Peter
____________________________________________

2004\10\26@065951 by Peter L. Peres

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On Mon, 25 Oct 2004, Lucian Copat wrote:

> Yes, you are right, I have to find another solution. Thank you very much for
> answering !

You can implement what you want using MCS51 compatible UARTs in 9 bit
mode. You get to write your own protocol.

Peter
____________________________________________

2004\10\26@075458 by Alan B. Pearce

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>You can implement what you want using MCS51 compatible
>UARTs in 9 bit mode. You get to write your own protocol.

Some of the PIC chips can do a similar 9 bit mode.
____________________________________________

2004\10\26@085839 by Lucian Copat

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face
Yes, I do have such a protocol implemented for the USART in the PICs, but I
was thinking of a more simple way to address multiple slaves at once. I gave
up with this idea and will address each device on the I2C separately.
Thank you to all who replied.

Lucian


----- Original Message -----
From: "Alan B. Pearce" <A.B.PearcespamKILLspamrl.ac.uk>
To: "Microcontroller discussion list - Public." <.....piclistKILLspamspam.....mit.edu>
Sent: Tuesday, October 26, 2004 2:57 PM
Subject: Re: [PIC] I2C Broadcast Question


> >You can implement what you want using MCS51 compatible
> >UARTs in 9 bit mode. You get to write your own protocol.
>
> Some of the PIC chips can do a similar 9 bit mode.
> ______________________________________________


'[PIC] I2C Broadcast Question'
2004\12\08@101049 by Buehler, Martin
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if you want to broadcast to a group of devices, simply give them
identical addresses.
if these are simple devices like parallel ports, this is no problem, as
they always give you an ack, so you don't need to detect it.
but make sure, you never read from such a group, as you will only read
bullshit.
tino

>{Original Message removed}

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