What you sometimes see in industrial motorcontrollers is a simple echo
method
works as follows

-all motors are chained
-motor 1's rx is connected to the computers tx
-motor 2's rx is connected to motor 1's tx
... etc...
-motor n's rx is connected to motor n-1's tx
-motor n's tx is connected to pc's rx ad thus completes the circle.

-all motors echo their input to their output except if the command is for
this motor only (there are broadcast commands possible which would travel
thru the entire chain)
-every motor has its own address and responds only to commands with the
right address embedded
-a motor can reply to messages which will echo thru the chain till they
reach the pc
-There is a special command that sets the motor's address and since this
command is special only the first device that does not already have an
address assigned it will not be echoed to subsequent devices this way the
entire chain gets addressed by subsequent address setup commands.

If you can live with the delays in this method it wrks fairly well

Kind regards
Peter van Hoof

----- Original Message -----
From: "Alan B. Pearce" <A.B.Pearce@RL.AC.UK>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, June 22, 2004 11:59 AM
Subject: Re: [PIC:] serial port dilemma - design advise requested


> >I have a PIC device that connects to my PC via serial port
> >for constant communication.
> >
> >I would like to have over 10 PIC devices connected to my PC
> >somehow for communication.
> >
> >However, i would not like to buy some sort of expensive
> >multi serial port card for it.
> >
> >What sorts of things can i do to over come this problem?
> >Potentially i would like to use over 10 of these PIC devices at once.
>
>
> I used to work on computer terminals that used a multi-drop RS232 levels
in
> a polled terminal environment. They did this by having a resistor that
went
> from the TX data line to -12V, and then pulled the line to +12V using a
PNP
> transistor. This transistor is used in place of the normal MAX232 type
> device. You then also need a suitable RS232 receiver at each PIC, but with
a
> higher input impedance than normal.
>
> You then need to work out a protocol where the software in the PC calls up
> each device in turn, telling it when to transmit the data to the PC.
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.