communication error with multiple slaves on RTU on same port

[medvdev]

Dear Mikhail,

Please clarify the behavior of communication lines, each communication line is a master ?? for the connected device for which it is created.

If say for “communication line 1” virtual “com port 1” is assigned, and data polling is done at an interval of 15 minutes, then during that 15 minutes period can other communication line use the same come port 1 if assigned so, as RS 485 states that multiple slaves can be communicated through same com port on multi drop network.

My observations are:-Communication line keep com port occupied irrespective of communication or not and other communication lines denied access to same com port even during no communication period.

Please explain then how to utilise rs 485 feature of multi drop communication.

Regards,

[Mikhail]

Please clarify the behavior of communication lines, each communication line is a master ??

It depends on a driver (Kp*.dll). In case of Modbus it is master.

can other communication line use the same come port 1 if assigned so

No, it is blocked.

Please, explain why do you need to share COM-port between different applications? Are there other approaches to solve your task?

[medvdev]

Dear Sir,

I would like to share the same rs 485 communication line to connect with other slaves, as rs 485 allows the multi drop feature. the gateway converter that i m using install virtual com port ( say com 1) on pc then communicate with any assigned device, now as communication is on 2 wire rs 485 line i want to communicate with other devices also using features of rs 485 i.e. it support multi drop network. on same wires, but communication lines keep the com port busy all the time irrespective of it is communicating or not.

Also one gateway (TCP to RS 485 converter) can install only one com port on pc, how to communicate with multiple devices on modbus RTU mode.

[Mikhail]

In this case you should add all the devices connected to RS485 to a one communication line of Communicator. It is a usual situation.

[medvdev]

Dear Sir,

I think It will not work, consider all identical devices…. how the data address will be identified then…. is it possible to assign multiple slaves address to single communication line??

Regards,

[Mikhail]

is it possible to assign multiple slaves address to single communication line?

Yes, each device on a communication line has its own slave address.

[medvdev]

OK… but at communicator when we go to request sequence tab, there at address field only one address can be assigned to any communication line, then how is it possible to communicate with more then one devices on same communication line.

regards,

[Mikhail]

Create a screenshot, please.

[medvdev]

https://postimg.org/image/jq00k97jb/ or

[%5D(https://postimg.org/image/jq00k97jb/)

I think , I am not able to explain you…. agian… can a single communication line talk with multiple devices simultaneously…… if yes then where to define the address of say 4 devices connected with single communication line,

in communicator as attached in link above only one device can be assigned to single communication line.( then how can one communication line talk with multiple devices at same time??)

[Mikhail]

You should add another device to the line. Use Plus button or import the device from the configuration database.

[medvdev]

How to add two device with one communication line…??? plus button add another communication line. can second device be added to same communication line which is already having one device linked with itself?

I have tried but it is seems not possible.

Regards,

[Mikhail]

Could you make a screenshot what button did you click and what result did you get?

[medvdev]

i think i got it…. trying at wrong place….nice help…. thanks.

[Author]

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