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How to know the SERIAL COM set up?

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I have to create a replacement of a control card; this card exchange data by modbus rtu (RS485); some of the registers are about SERIAL COM set up (baud rate, ID, parity etc)...I know how to have the ID...but how to have the others values in the Unilogic?


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  • MVP 2023

Orso, I think a bit more information is needed.

However, many of the 485 devices I use have a special program available for setting the device's comm parameters, and then they stick.  The various programs work by using communication parameters that are not normally available in modbus.  Once you have changed the factory settings using said programs, you then can get into them via normal modbus means, including changing basic comms settings.  It can be frustrating because of this need, but on the other hand it is good in that you have to pre-program the unit and then it's done, ready for install on the line.

Perhaps I've misunderstood the question, but why do you need to be setting comms parameters via the plc?

cheers, Aus

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  • MVP 2023

I used the vision controller to create a replacement for a modbus device that is no longer produced and has a strange custom command system.

Accordingly, all requests to the device (vision) were perceived as a string in which the controller determined what exactly should be transmitted in response. The only standard tool that helped me was the automatic calculation of the message-response checksum. At the same time, I was forced to ignore the checksum of the incoming message.

The device still works in the system instead of the stock chiller controller. It gives the system the correct coolant status values to ensure a safe start. This is a bit unusual decision. But without this controller, the entire multi-thousand-dollar machine was a pile of scrap. However, I had documentation that described all the exchange commands with the cooler with examples.

I think you understood my tip about your device. That is, you need to write your own data exchange, creating the illusion for the outside world that the PLC is a card that you change.

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Hi all

thanks for answer...ya maybe my "request" is not so clear...i try again...so...I am creating a replacement of a contro card; the original card can exchange data with SVS/external controller by modbus rtu; so for example has registers from adress "0" to adress "1000"; some of theser registers return the value of "process temperature", "process step", "alarms" etc...some of these return (read only) how the RS485 port is set up (ID, baud rate, parity)...in the unilogic when I create a modbus Slave istance a struct is automatically created in the global tags...in this struct i have the ID of the slave but nothing about baud rate, parity, bit format, stop bit....what tags, available for the ladder, have these info in the unilogic?

i don't need these to configure the rs485 port (i know how to do) but I need these to fill modbus register and made these info available.

honestly I don't know if these modbus register will be really requested/used from third party externa control (SVS etc) but these are available in the exchange data document...so I have to implement...obviously I can set a static value but this means that I will exchange "fake" data.

hope that is more cleare.

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