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Panel PC Modbus Network

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gothomas
Posts: 26
Joined: 27/05/2019, 23:11

Panel PC Modbus Network

Post by gothomas »

Hi,

I am currently setting up a project that has 95 nodes on the modbus network.
If all nodes are powered up and connected on the modbus network and have been correctly addressed, when the TD900 soft plc is started all nodes will be connected and communicate okay.

However if one of the nodes is not connected when the TD900 soft plc is started, but is connected after the plc is running. This particular node will not be seen on the network.

Do i need to reboot the plc for this node to come back online?
Is there a way to force the node back online without rebooting the plc?


Thanks in advance for your support.
Pixsys tecnico 6
Moderatore
Posts: 1184
Joined: 12/09/2016, 14:49

Re: Panel PC Modbus Network

Post by Pixsys tecnico 6 »

Hi,
If the Modbus RTU protocol is used, at least one register reading of the slave node must be carried out to reactivate it. Are the Slave nodes that are switched on after the PLC only "written" by the TD900 or do they also have a read-only register? As a solution you could read a register every few seconds for each node. If the node is online it will respond to the TD900 that will put the node back online. For example you could read the firmware version of each node, but any other node register is fine.

Best regards.
gothomas
Posts: 26
Joined: 27/05/2019, 23:11

Re: Panel PC Modbus Network

Post by gothomas »

Hi,

The particular nodes i am using are all MCM260-3AD.
so they have both read and write registers.

Is there a node status variable that i can use in my program to indicate if a node does go offline?


Thanks.
Pixsys tecnico 6
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Posts: 1184
Joined: 12/09/2016, 14:49

Re: Panel PC Modbus Network

Post by Pixsys tecnico 6 »

Hi,
the bool variable of the Array SysMbNodeStatus (file attached) is the status of the Modbus Slave Node RTU.
LogicLab_sysMbMRtuNodeStatus.PNG
How to use:
LogicLab_sysMbMRtuNodeStatus_CAD.PNG
Best regards.
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gothomas
Posts: 26
Joined: 27/05/2019, 23:11

Re: Panel PC Modbus Network

Post by gothomas »

Hi,

I am currently having an issue with the modbus network from a TD900 V2 panel.
I have tested the network with a second panel and all appears to work fine.

The fault that is occurring is intermitting, the modbus network appears to stops working. the outputs switch off, but if i check the output in the watch window of logiclab it will be TRUE.
It will remain unresponsive for approximately 10 to 15 seconds and then start working again.

Any ideas as to why?

Thanks.
Pixsys tecnico 1
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Posts: 1649
Joined: 29/10/2010, 10:09
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Re: Panel PC Modbus Network

Post by Pixsys tecnico 1 »

IT could be an hardware issue, so check dip-switch configuration of the TD900, the Dip-switch are located near the green terminal blocks (you must remove it). Check if the dip-switch configuration are the same for both TD900s.

In any case, a delay of 10/15sec could be packets missing events, so check the Array "SysMbNodeStatus" in the watch windows to see which controller are missing in that moments.
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