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Using (2) MD4 Display modules and (3) MC43

Mark 1 year ago in IQANdesign • updated by Ulrik Zakariasson (Software development) 1 year ago 2

I have an application that will use (2) MD4 display modules active at the same time for the screen space as well as (3) MC43's for the I/O points (without using the Master capability). Basically I want to use the MC43's as expansion modules. Is there any reason I cannot do this? What are the recommendations to make this work?

Hi Mark,


Using several master modules in an application is not an issue, but there are a few things to keep in mind. 


1. CAN bus load on the CAN buses used for inter master communication as is with any CAN bus with multiple modules. You don't want to have CAN traffic at a level that will overload the bus, also keeping in mind CAN bus loads can spike from time to time depending on several factors. 

2. There is one master considered the "Head Master" and will have the address of 0.  Only one master can use the address of 0.

3. The workload of handling system logic can be distributed as desired, i.e. on one master or multiple masters.

+1

We are doing exactly this.  The master bus alone cannot exchange enough information between modules as it requires one can frame per variable.  We have used a dedicated j1939 500 kBps bus to exchange data between modules and the master bus for only emergency stop etc.  Messages (data) must be sent out and received manually  from/to each module on this j1939 bus (making a variable public only makes it public on that one master module).


The problem with this method is that it will not simulate in IqanSumulate and thus requires more physical testing. 


Otherwise this method seems to work fine.  It also allows modules to be able to run low cycle times (5 ms for instance) for those functions that will benefit from faster calculations, and other modules (displays for instance) can run 50 ms (allowing processor time to display cameras images etc.).