MVI56-MNET ModbusTCP/IP
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richywiseman
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Monday 31 October 2005 4:17:42 pm |
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MVI56-MNET ModbusTCP/IP
I have an application in which I communicate whith 14 VSD's(Robicon) using Modbus TCP/IP and everything works fine, except I have the following problem.Everytime a drive is powered up I cannot initaite comms with it until I coldboot the module. This is very frustrating and I need to be able to leave the system with the client knowing that if he powers down a drive that comms will be re instated without resseting the card.
Has anyone came accross this?
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jsanders
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Tuesday 22 November 2005 3:43:53 am |
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RE:MVI56-MNET ModbusTCP/IP
This sounds like a problem related to the way the MNET modules maintain and update their internal ARP table, the scratchpad that matches IP addresses with hardware MAC addresses. Once a socket has been opened to a device, the ARP table entry is updated and used whenever a command needs to be issued to that device. If a command is sent to a powered-down device, the command will time out, causing the module to reissue ARP requests to try to locate the target device. If it cannot do so, it will stop trying for some significant amount of time or until it is rebooted. Simply re-applying power to the target device will not cause the module to update it's ARP table. It takes a reboot to do that.
Our best recommendation would be for you to train your end-user to reboot our module every time after he repowers a target node that had been powered down. This will shorten the time before the module will again try to send commands to that node.
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