Sharing RS232 Modem between two devices

I have two machines, and 1 modem ( uses RS232) and I would like to share this modem between the two machines, what do I need to accomplish this ? has anybody done this before ?

Rabie K … ilType=Top

Thanks Awneil,

will that work if I setup the two machines to call out at different times. without any interference.

in case of Machine A initiate the call and connects to the network and send AT commands, how can I let machine B wait until Machine A finishes or Line is not busy anymore ?

Do you have a suggestion ?


Speak to their pre-sales technical support people and discuss your requirements with them!

I think they use the flow control signals to “block” one device while the other is using the modem…?

I did order one item for testing and I will give some feedback in case somebody else have the same situation where he has to share a modem.

Rabie K

The device costs almost as much as the modem cost.
I have two Machine A and B and the Modem.
If Modem is hooked up to Machine A and Not B :
Machine A sends AT command, modem respond.

If Modem is hooked up to both Machines ( A and B ) :

Machine A sends AT command, no response.
Machine B sends AT command, no response.

I don’t know what will be the ideal solution to share a DB9 connection.

Indeed - so why mess about trying to share 1 modem?!
Why not just get 2 modems?

Whatever you do otherwise is just going to be a kludge!

For production perposes buying 10000 modem is different than buying 5000 plus SIM cards and their data plans.
So I am trying to cut some costs, and look for a simple solution that I can benifit from.

The fact of the matter is that modems are simply not designed for sharing - an RS232 link is designed to be a simple, point-to-point link.

So it’s unlikely that you will find a solution that is both simple and reliable for volume deployment in the field!

Have you considered a Fastrack with two serial ports?

What are the “machines” that you are connecting? Can you have just one of them connected to the modem, and the other links to it?

+-----------+               +-----------+
|           |               |           |
| Machine 1 +---------------+ Machine 2 |
|           |               |           |
+-----+-----+               +-----------+
|           |
|   Modem   +
|           |