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PICList Thread
'Plug-and-Play'
1997\05\05@112120 by Antonio Almeida

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       Does anyone has some ideas on how to do a poor man's version of
Plug-and-Play ? I need it to implement a network (maybe using RS485), and
i want to insert nodes automatically, without the need for the person who
plug's the node to know what's happening. Any ideas, comments ?...

Thanks,
Antonio Almeida

1997\05\05@132710 by Andy Kunz

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At 03:37 PM 5/5/97 +0000, you wrote:
>        Does anyone has some ideas on how to do a poor man's version of
>Plug-and-Play ? I need it to implement a network (maybe using RS485), and
>i want to insert nodes automatically, without the need for the person who
>plug's the node to know what's happening. Any ideas, comments ?...

Good luck!

Let us know how it turns out.

FWIW, PnP is universally referred to as "Plug-and-PRAY!"

Andy

======================================================================
Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865 USA
             Electronics for Industry & R/C Hobbyists
        "Go fast, turn right, and keep the wet side down!"
======================================================================

1997\05\06@050649 by Keith Dowsett

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At 15:37 05/05/97 +0000, you wrote:
>        Does anyone has some ideas on how to do a poor man's version of
>Plug-and-Play ? I need it to implement a network (maybe using RS485), and
>i want to insert nodes automatically, without the need for the person who
>plug's the node to know what's happening. Any ideas, comments ?...
>
>Thanks,
>Antonio Almeida

Hi Antonio,

  Have a look at the way ARCNET handles this problem. It's pretty good
providing you don't insert or remove nodes very often. It's on the SMC web
site somewhere, a web search should find it.

In short what they do is have a token which is passed around among the
nodes. When a node has the token it can initiate a transmission or pass the
token along to the next numbered node.

When a new node is added it will realise it is not getting the token. It
will then wait until the token is being passed and pull the network down,
destroying the token. The nodes then start counting until the lowest
numbered node times out and creates a new token. It then looks for the next
node to pass it along to which in turn passes it to the next and so on. This
process reconfigures the network to include the new node.

Quite neat, for a peer to peer network.

Hope it helps,

KEith.



==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail: spam_OUTkdowsettTakeThisOuTspamrpms.ac.uk
  WWW: http://kd.rpms.ac.uk/index.htm

1997\05\06@131758 by paulh

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On Mon, 5 May 1997 15:37:27, Antonio Almeida <.....deec352KILLspamspam@spam@TOM.FE.UP.PT> wrote:

>         Does anyone has some ideas on how to do a poor man's version of
> Plug-and-Play ? I need it to implement a network (maybe using RS485), and
> i want to insert nodes automatically, without the need for the person who
> plug's the node to know what's happening. Any ideas, comments ?...

Dallas Semiconductor, http://www.dalsemi.com, has a slow 1 wire protocol
that allows a master device to probe the bus and find all the devices.
Each chip that supports the protocol has a unique serial number.  You can
impliment the protocol with a PIC and RS-485, as long as the RS-485 has a
pull-up resistor, so the idle bus always goes to the same logic level.

You need to make sure each device has a unique serial number, or the
scheme fails.  You'll also need some information describing the board
configuration.  An easy way to do it, is to include a Dallas Semiconductor
part with eeprom on your board.  Use the part's serial number for the
board's serial number and the EEPROM to hold the board configuration
information.  I think the DS2430A would work, if 32 bytes of eeprom is
enough to store your config info.

You can do the same thing with just a PIC, if it has EEPROM, or even OTP,
as long as your manufacturing folks can store unique information in each
PIC.

--
paulhspamKILLspamhamjudo.com  http://www.hamjudo.com
The April 97 WebSight magazine describes me as "(presumably) normal".

1997\05\12@173823 by Steve Smith

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This is possable using three lines from pic to LTC485 devices.
connect 485 with the transmit enable turned off by pull up and controlled by
the pic the resistor keeps the transmit disabled while the pic gets going.
Using one device to generate a start bit all others then listen for the start
bit and transmit their information in a time slot in sequence. I have used
this reliably up to 19.2KB and 6 devices. (the 5 which are not masters spend
most of their time listining). Dont forget to randomise the wait time if the
data bursts are a long time appart (TMR0) works, otherwise they will never
sync. Been there got the T shirt..

Steve.......

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