Multiplexing the MDLC protocol


Thread Starter


Hi all,

I am looking for a product which I can use for multiplexing the MDLC protocol. This protocol is used by the Moscad RTU of Motorola.
I believe tha tthe MDLC is a protocol specific to the Moscad product line made by Motorola and is used primarily to communicate between Motorola Moscad (Moscad, Moscad-L and Moscad-M) product lines. I have not heard of any other device which uses their protocol, but you can contatc Dan Giedt at TLEC 303-697-0440 and ask him directly or contact Motorola to find out.

What is that your trying to do that you need to multiplex their protocol? You could use another Moscad, but I don't understand what your after.

Matt Hyatt
Hi Matt,

I need to access to one RTU from multiple Masters. I need to connect two line modems and one Dialup modem to one RTU which is normally slave. And as that CPU has got only 3 ports and I am in need of further ports for local communications in Modbus. I need a multiplexer which has got 3 MDLC "slave" to 1 MDLC "master" where master and slave are not really slave and master as this protocol works different.


Motorola supports multiple masters, addressed as 1600-primary, 3200, 4800, 6400, ect as secondary) each master can then poll the RTUs for data or they can be updated by another master. You probably want to diagram your network out first because it sounds like your making it to complicated. Normally you have a master which polls MDLC to the RTUs, the master than communicates via Modbus to a host computer running Wonderware, Intellutions or whatever SCADA package you desire, if you need the same data at other computers, set them up as view nodes and then pipe the Modbus data to them.

Typically CPUs for Motorola have a dedicated port for RTU/FIU communications (port 3), which could be a wire line modem, (2 or 4 wire), RS-232 port, RS-428 or radio. Port 1 can be RS-485 or RS-232 and port 2 is RS-232. You can also put a radio concentrator card onto port 3 and have 4 CPU's control 1 radio. So what is the link between FIU and RTU?

You can also drop in another CPU where you need it to handle the extra port requirments and have direct MDLC to the other FIUs. Typically I have not seen RTUs set up to handel Modbus locally, but it can be done, you of course lose a port for that.

You may want to get in touch with TLECC, they are Motorola experts - ask for Mike Richardson or Dan Giedt - 303-697-0440.

Any thing beyond this basic discussion, contact me offlist at my email address, if your state side send me your fax number I will draw a possible configuration out for you, also send me the exact equipment you have and how you anticipate interconnecting the system.

Matt Hyatt
Technical Consultants
[email protected]