DH-485 Network MSG command help

Hello all:

A while ago, my partner Sean and I (college students) had posted on the forums for help setting up our DH-485 network. We are trying to use the MSG command between PLCs. Is there a way to use it to turn on/off an output? We have tried a few different techniques, but no success. Is there a trick to it?

We have tried sending an integer (N7) from one PLC to another, but this does not work. Under the setup menu, what do we need to put under the following blanks:
-----------------
Write PLC:
This Controller:
Data Table Address____________
Size____________

Target Device:
Data Table Address____________
Local Node Address___ (is this the node that we want to send the value to?
-----------------
Read PLC:
This Controller:
Data Table Address____________
Size____________

Target Device:
Data Table Address____________
Local Node Address___ (what would this be for?)
-----------------


Please let us know what we should try, or possibly, post a link to some sample code on the web.

Many Thanks!
-Teo & Sean
Millersville University ITEC students

Write PLC:
This Controller:
Data Table Address____________ Data source, in this case N7:0
Size____________Number of words to send starting at N7:0

Target Device:
Data Table Address____________Location of written data, such as N10:0
Local Node Address___ (is this the node that we want to send the value to?
----------------- Yes this is the Node address of the "target"

Quick Question

Ken:
Thank you for your prompt response! We are gaining a better understanding already. A quick question:



Target Device:

******** IS THIS THE TABLE LOCATION WHERE THE DATA WILL BE SENT ON THE PLC WITH THE BELOW NODE NUMBER?*********


Data Table Address____________Location of written data, such as N10:0



Local Node Address___ (is this the node that we want to send the value to?
----------------- Yes this is the Node address of the "target"


********************************

Also, do you have to enter the data into the N7 table manually to send it?

You can use any ladder logic function to move, copy, add, subtract etc... To get the desired data in a register. I used N7:0 in my example, but it could be F8:0, N17:0, any register....

The MSG instruction just passes along the current value when the MSG instruction is executed.

The data table address in the Target PLC, is the starting address for you transferred data. This also can be almost any register. In my example I used N10:0, but it could be any valid data table address.

As an experiment, if you mapped all the I/O in the local PLC to a register and then messaged that register to a remote PLC and mapped the outputs you could engergize a local input and see the remote output respond.


Let's say your local PLC (node 1) had a 16 point input module located in slot 1, and your remote plc (node 2 ) had a 16 point output module located in Slot 2.

In the Local PLC, use the MOV instruction to move I:1.0 to N7:0. Then use a MSG write to send the local N7:0 register to the remote N10:0. Use the MOV instruction to MOV the value of N10:0 to O:2.0.

LOCAL LADDER:






TARGET PLC:

Ken:
Thank you for all of your help! Your post provided us with a direction to our solution. We had to change a few minor things, but we understand everything now.
-Teo & Sean

Glad to be of service.