Hi,

I got two questios:

There are two slave devices(SEL-787) from which I should read data via MODBUS RTU.

I checked SEL-787 manual and it says it supports EIA -232 , but my collegue order

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Should we change order to:

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Hello,

pls check again your Slave real devices which interfaces they have for sure. If they have only RS-232 available for MB RTU, this can be problem. I think your solution with RS-485 CP module is right, because you can put more Slaves on one bus, but if RS-232 media is selected only one device can working on one line. You can't simply here change CP341 RS-485 to RS-232 because in this case you'll need 2 CPs RS-232 because of my mentioned media system. Try check Moxa's Solutions if they have some serial adapters that can have on one side RS-485 port and on other side of adapter 2 RS-232 ports, controlled with some system, but pay attention how this adapter differ signals. Only my idea.

Duris_I

Hello,

pls check again your Slave real devices which interfaces they have for sure. If they have only RS-232 available for MB RTU, this can be problem. I think your solution with RS-485 CP module is right, because you can put more Slaves on one bus, but if RS-232 media is selected only one device can working on one line. You can't simply here change CP341 RS-485 to RS-232 because in this case you'll need 2 CPs RS-232 because of my mentioned media system. Try check Moxa's Solutions if they have some serial adapters that can have on one side RS-485 port and on other side of adapter 2 RS-232 ports, controlled with some system, but pay attention how this adapter differ signals. Only my idea.

 Wait, so If its RS-232 only one slave can be connected with Master, no multiple slaves?

Yes I checked Slave device, RS-232 comes with default, for RS-485 its essential to order additional part. 

Our current CP RS485 is not compatible with RS232 slave.

So option is to change CP to RS232 but since you have said 2 CP's for 2 slaves are necessary

the best option would be to order additional part on Slaves to support RS485

Hello,

exactly, better is order RS-485 Interface for your real Slaves devices. Only idea, you're familiar with dongle for CP341 with RTU Master selected? You need it for your CP341 MB RTU Master solution.

Important update: I ask also about that, because due your ordered CP341 CH00 is important which SW you're use also for programming, because if you're on TIA, this is another problem.

Duris_I

Hello,

exactly, better is order RS-485 Interface for your real Slaves devices. Only idea, you're familiar with dongle for CP341 with RTU Master selected? You need it for your CP341 MB RTU Master solution.

Important update: I ask also about that, because due your ordered CP341 CH00 is important which SW you're use also for programming, because if you're on TIA, this is another problem.

Nope, I'm not, but now I searched a little bit on forum and it looks like beside

I need to order 6ES7870-1AA01-0YA0- dongle (Master) plus CD software too

Hello,

yes, dongle is required, ask your Siemens support for exact info. But as I asked about CP341 CH00 and your SW, this is another possible problem.