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Sunday, October 20, 2019
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Issue with Modbus Communication
Issue wth PLC as Modbus Master and 6 HMIs as slaves on Rs485

Hello friends,

I am having a PLC as a Modbus master on serial 485 connected to 6 HMIs as slaves. I read from and write into the HMIs registers by the PLC. The application is for a passenger elevator with Ground + 4 floors. All these floors have an HMI as a LOP device (Landing station operator panel) and another HMI in the Car Cabin as the 6th HMI. The problem I face is Destination Calls are registered without WITHOUT a request made from either the LOPs or the COP. The programming is done in Basic Language. Can someone advise me how to overcome this problem.

Thanks in advance.

Regards.
Vilas Desai.

I'm not sure what the "destination call" consists of, but for automation it needs to be some form of electrical signal. Tie that electrical signal into the PLC and let PLC logic do its thing. If the HMIs need to be updated, then the PLC had the data to update the HMIs.