2 modems to Micrologix 1200

I have a micrologix 1200 with 2 comm ports.
1 is connected to an easy touch OI using DF1
The other is connected to a RF modem messaging to another micro 1200 and is also connected to a dial up modem for remote access.
I have the 2 modems connected to the same port thru a Black Box nonpowered port sharing device. I have a problem when going online with the dial up modem the message instruction thru the RF modems locks up with communication error. First is there a better way to share this port. Second does anyone have any idea what I might be doing wrong.
I have been programming several years, but due to a recent job change am new to remote comms. Any references would be welcome.
Thanks
John Rogers

You need to use a multiplexer that allows DF1 messages to be properly routed. Black box does not deal with DF1 in any way.

Go to www.tomantron.com and look at modem examples.

I have not used a modem with the ML, but have used both barcode scanners, and printers.
On one job with two scanners and two printers, I used a relay on the serial lines to switch between the scanners and the printers.

Thanks to both of you.

Jiri, The muxi port is the device I have been hoping to find. Will order as soon as approval is received.

RoTa Tech, your advice is very clever. I will certainly experiment as time allows.

This was my first post and I'm already impressed with the results.

I will share my knowledge as others have questions I have experienced.
Thanks
John