Subject:
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Re: Comuniction with PC (2)
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 17 Jun 1997 16:56:29 GMT
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Original-From:
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Bastiaan Jansen <B.S.H.Jansen@student.=avoidspam=utwente.nl>
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Viewed:
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1589 times
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Hi,
well that's a cooncidence. I'm working on a project witch multiple nodes
via RS-232 also. We use a philips microcontroller(well 3 actually), but
that doesn't matter for the RS-232 communication.
We found a method to make it possible for all nodes to communicate with
eachother, but if you simplify it a bit you can also use it to make it
possible for multiple nodes to communicate with one node only.
I'll adapt it to your situation with handy boards and one pc:
First convert the RS-232 signal from the PC to TTL level using a MAX232
(you can see how to connect it in the HB charger interface schematic). Put
the MAX232 between the TxD and RxD line (as in the charger interface).
Connect the converted TxD line from the pc to the RxD pin on all
handyboards. (maybe a buffer is needed to drive these 8 inputs, but I'm not
sure of this because our application is a bit different).
Now connect all 8 TxD lines from the handyboards to a AND gate and connect
the output of this and gate to the MAX232 chip. The MAX232 can now convert
the signal back to normal RS232 voltage levels for the PC. Since the TTL
RS232 signal is asserted high, the AND gate wil operate as an OR gate. So
all inputs are OR-ed to the PC. The PC can thus receive all nodes.
(Note: all RxD and TxD lines of the HB I mentioned before are unconverted,
so NO charger board is attached.....)
All you have to do is to build a CRC check (or something alike) in your
code to check if the received packets are correct. If they are not, you had
a collision and they have to be resend....
Of course you also have to send some adresses and other crap....
Hope you get the idea,
Contact me if you have more questions,
Bastiaan Jansen
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> From: German Pablo Gentile <ggentile@cvtci.com.ar>
> To: handyboard@media.mit.edu
> Subject: Comuniction with PC (2)
> Date: dinsdag 17 juni 1997 15:16
>
> I'm developering a project . This project need comunication from Pc to 8
> Handy boards(outside of IC, i'm working with Delphi). My problem is : How • i
> can comunicate with 8 handy , without collitios???. Well , i think in • send
> message to all the handy via rs-232 , with a header telling wath number • of
> handy receive the message, and via software the correct handy board • receive
> and discriminate the message. My problem is inthe reverse way, when the
> handys send message to the PC... In this way can happen more of 1 • transmit
> at the same time!!! I think a solution may be , 8 input board and when • one
> transmitt the other inputs don't receive message. But I have not idea how • i
> can drive that. Please any help or idea , i have thanks for ever.
>
> I have to say this always, sorry for my poor english !!!
>
> German Gentile
> ggentile@cvtci.com.ar
>
>
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