read/write MSG in project file

idowulawrence

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Apr 2010
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Hi guys, having concluded to use MSG instructions to exchange data on dh+ I need more enlightment as to how to use MSG instructions to write from a node to some nodes (5 of them) while reading from these same nodes simultaneously. There are some tags to be read from these nodes everytime (time-critical) while there are some tags to be written to them, how do I configure these procedures without causing communication conflict. Also the dh+ network is to interact with the HMI, can the HMI just poll data irespective of the comm procedure accross the network of other nodes?
 
I would recommend setting up a polling routine that executes one message at a time. After the first message has executed and you have recieved either the done bit or the error bit, move to the next message and so on.

I have seen systems where multiple messages are fired off at the same time. These are usually the systems that have communcations problems as mutliple messages can really hammer a network.

As for the HMI polling rate, it depends on what HMI you are using but you can probably set the update rate for each screen or maybe for each tag. Setting the update rates higher where available will help reduce the HMI's impact on the network, especially if the PLC to PLC messages are more critical.
 
That s fine, i will try that, meanwhile my HMI is wonderware intouch 10 with Rxlinx driver, unit tag's update cannot be set here .May be I should use Topserver OPC server as comm server?



blamb said:
I would recommend setting up a polling routine that executes one message at a time. After the first message has executed and you have recieved either the done bit or the error bit, move to the next message and so on.

I have seen systems where multiple messages are fired off at the same time. These are usually the systems that have communcations problems as mutliple messages can really hammer a network.

As for the HMI polling rate, it depends on what HMI you are using but you can probably set the update rate for each screen or maybe for each tag. Setting the update rates higher where available will help reduce the HMI's impact on the network, especially if the PLC to PLC messages are more critical.
Click to expand...
 

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