Rs232

Can One have a multidrop network with RS 232 standard by looping???

My situation is, I have one computer and 7 RS232 devices and I have actually done a daisy chain network with one unique ID for each device... for every transaction with a different device I change the ID, so it is like a point-to-point communication...

I am aware that RS 422 and 485 are recommended for looping network, with the protocol as required, but can I find some documentation where RS 232 is ??? Or otherwise if it is not, some literature stating likewise !!!

In theory I think you could do it.
But you would have to keep the entire daisychain within the 15 meters that is the maximum for RS232.

Not knowing which protocol you would be using, I assume that it must a master-slave type network.
You must connect the Tx of the master to the Rx of all the slaves, and the Rx of the master to the Tx of all the slaves.

But I doubt that it will work. Good luck with it.

Thinking again...

MAYBE you can put all Tx and Rx pins together on the same connection.
So that you have a common GND and a common Tx/Rx on each device.
In that case a half-duplex token passing type network protocol could be used.

Would like to know how it goes

How???

Thanks for the replies Jesper,...but how will tying up all the Tx together and Rx together work???

Ther'd be a conflict of signals at the pins in the port of each device, even when we use a token passing protocol, wouldn't there??
My earlier configuration is working on the same lines as your first suggestion... there is a problem with the speed and at best not reliable...

My problem here is, I've got to show to a %&*$ customer that RS232 by design does not allow multidrop, but I cant find literature to support my statements... Can you help???

If there would be a conflict depends on the protocol.
A protocol that "expects" a two-wire RS485 connection will know that it can "hear itself" on Rx when it transmits on Tx.

I doubt that you can find some specification that states "do not use RS232 for multidrop" but you can find specs that says that RS232 is intended for point-to-point connections. Try "RS232 Specifications" on Google.

RS-232 will only work in a multi-drop enviornment if the devices are way non-standard 232 devices. Or, if they have two rs-232 ports and re-generate signals between them.

RS-232's problem in multidrop is that it is an "ALL ACTIVE" physical layer (not the protocol, but the actual wiring). All drivers are either high or low, they can't be tri-stated. Some manufacturers try to get around that in a limited fashion by padding the signal lines with series resistors, but that isn't a true solution.

Try BlackBox for small, self-powered 232/485 converters.. here is one I use all the time here:
ftp://ftp.blackbox.com/manuals/i/IC620-623-624A 9-03 Manual.pdf


If that whole link doesn't work, the partial is:
ftp://ftp.blackbox.com/manuals/i
and converter is IC620-623-624 9-03 Manual.pdf

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In some cases, you can do multi-drop broadcast (one master to many slaves) or multi-drop addressable broadcast (one master to one of many slaves), but multi-drop bidirectional RS232 is a hack at best.

Good luck.

rdrast,
I see what you mean.
A "zero" is actually -15V and "one" is +15V (or is it the other way round ?). So connecting them all together will make a real good mess.

Well, Thankyou for the discussion Jesper and RDRast... Even if nobody else is...but I am convinced that RS232 would not really solve my(customer's in this case) issue of multidrop!!!!

I think the safer and more reliable option would be to go for RS485...
Thank you very much!!!!!