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PICList Thread
'PIC networking'
1997\01\27@105612 by ermott

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I haven't looked closely at what would be involved but perhaps
you could interface your PIC's through RS485 drivers.

-This is in response to Craig Houston's question about networking PIC's.

1997\01\27@120017 by John Dammeyer

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At 10:55 AM 27/01/1997 -0500, you wrote:
>I haven't looked closely at what would be involved but perhaps
>you could interface your PIC's through RS485 drivers.
>
>-This is in response to Craig Houston's question about networking PIC's.
>

Hi all,

I just finished a PIC Master/Slave interface.  Used RS485 devices two wire
1/2 duplex.  Master Polls slave and if slave address matches then slave
responds.  Network software had intercharacter timeouts and packet timeouts.
I used a LF character as a Start Of Packet (SOP) and a CR character as an
End Of PAcket (EOP).  Data was restricted to 7 bit ascii although some key
characters did have their eigth bit set.  Ie: data could never be confused
as SOP.  Any new unit appearing on the network synchronized itself by
waiting for the SOP.  If electrical noise simulated a SOP char (0x0A the
linefeed char) then the next char had to arrive within 5ms or else the
entire message was trashed until the next SOP.  If electrical noise
simulated an EOP then the rest of the message would be ignored because it
did not contain an SOP.  Receieved message length would be wrong, (fixed
size packets), as would checksum,  so this system was fairly robust.

John

1997\01\27@121040 by calladus

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I'm also interested in connecting PICS in a network environment.  I
would like to use a Hub based environment using the RS-422 protocol, but
I haven't found the protocol standard yet.  Anyone have any ideas on
where to find these protocols?  I've heard that they must be purchased.

 -calladus-


---------------
Andrew McDermott wrote:
>
> I haven't looked closely at what would be involved but perhaps
> you could interface your PIC's through RS485 drivers.
>
> -This is in response to Craig Houston's question about networking PIC's.

1997\01\28@090849 by Ben Allgor

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>calladus wrote:

> I'm also interested in connecting PICS in a network environment.  I
> would like to use a Hub based environment using the RS-422 protocol, but
> I haven't found the protocol standard yet.  Anyone have any ideas on
> where to find these protocols?  I've heard that they must be purchased.
>

RS-422 is an EIA standard for the " Electrical Characteistics of Balanced
Voltage Digital Interface Circuits".  A standard for the signal
levels, impedances, protection,  etc. It can be used with any
protocol or digital signal.   RS-449 may be more help to you  it
covers  37 pin and 9 pin connectors, pinouts and other interface
items for serial binary data.  If you want to get a copy it is available from,

The Electronic Industries Association
2001 Eye Street
Washington, D.C 20006

Ben
---
C. Ben Allgor, PE
Benjamin Engineering Consultants
http://members.aol.com/bengineers

1997\01\28@114925 by John Dammeyer

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At 09:12 AM 28/01/1997 +0000, you wrote:
>>calladus wrote:
>
>> I'm also interested in connecting PICS in a network environment.  I
>> would like to use a Hub based environment using the RS-422 protocol, but
>> I haven't found the protocol standard yet.  Anyone have any ideas on
>> where to find these protocols?  I've heard that they must be purchased.
>>
>
>RS-422 is an EIA standard for the " Electrical Characteistics of Balanced
>Voltage Digital Interface Circuits".  A standard for the signal
>levels, impedances, protection,  etc. It can be used with any
>protocol or digital signal.
>C. Ben Allgor, PE


The RS422 is full duplex in that you have four wires instead of two.  In a
master/slave you tend to have the master speak and slave listen,  then the
slave speak and the master - and perhaps all the slaves listen, then the
master again.  For most protocols there is no major advantage to going with
RS422.  This is why RS485 using the 75176B has become so popular.  As for a
given message protocol; what works for one project might be terribly
inefficient for another.  If you are interested in a family of messages you
might look at SECS/GEM used in the semiconductor industry for factory
automation.

It was designed for RS232 single unit to single unit but there are some good
and bad ideas there and I've always felt that I can learn more from someone
elses bad ideas than from studying a good idea.

Regards,

John




Pioneers are the ones, face down in the mud,
with arrows in their backs.
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1997\01\29@090415 by Alexey Vladimirov

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27 Jan 97, Craig Houston writes to All:

P> I was wondering if anyone out there had any information on hooking up
P> PICs in a network like structure.

P> My plan is to have a bunch of PICs controlling various things, at
P> different locations throughout the house, and wanted to link them all
P> up - short of using a master PIC with all Tx / Rx lines from each PIC
P> going into it, I thought a network topology would be best.

What speed is necessary for your application ? For low-speed technology
(till 1200 baud) we made one interesting solution:

All local controllers connected via 2-wire line and powered from the same
wires. Controllers number depends from their supply current and
in most cases could be in range 50...500. Total wire length could be up to
one kilometer (about 100 baud in this case). Total supply current for all
controllers should not exceed 300...800 mA.

System consist from one master controller and till 500 slave controllers.
Master controller power all slave controllers and transfer data to all
slave simultaneously by switching line polarity. Slave can transfer answer
to master requests by short-time line shortenings.

We install some working netwoks, based on this technology in various
applications: guard systems, home gas and water counters, sensor networks, etc.

I plan to made some kind of application note available in near future.

Alexey Vladimirov  spam_OUTavladTakeThisOuTspammail.ormix.riga.lv

http://www.ormix.riga.lv/eng/mchip/mchip.htm
more than 300 PIC-related Net resources now...


'PIC Networking'
1998\12\28@091058 by Darkness
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Hello ,
     I am about to start a project where i would like to network two or
three PICs together, all the pics will be on the same circuit board.
Does anyone have any information or links to implementing RS-232, I2C
and RS-485 ??? (on PIC16F84)

Thanx
 Tim

1998\12\28@130028 by Andy Kunz

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>      I am about to start a project where i would like to network two or
>three PICs together, all the pics will be on the same circuit board.
>Does anyone have any information or links to implementing RS-232, I2C
>and RS-485 ??? (on PIC16F84)

Are they going to share the same pins?  Then either I2C or RS-485 is
appropriate.  Since you aren't using comm hardware, it really doesn't make
much difference.  You want an address-based protocol (which is your software).

Don't you have a real name yet?  Sure, we see "Tim" in the sig, but why not
in the "from"?!?!

It's just a pet peeve...

Andy

==================================================================
 Andy Kunz - Montana Design - http://www.users.fast.net/~montana
==================================================================

1998\12\28@131059 by Gerhard Fiedler

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At 21:31 12/28/98 +1100, Darkness wrote:
>      I am about to start a project where i would like to network two or
>three PICs together, all the pics will be on the same circuit board.
>Does anyone have any information or links to implementing RS-232, I2C
>and RS-485 ??? (on PIC16F84)

you don't need rs232 or rs485 levels if you stay on the board with the
signal. i2c is nice because it allows every pic to be master or slave, but
it takes a bit more software than simple asynchronous serial com. you find
most of this (i2c master/slave, serial rx/tx) in microchip app notes.

ge

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