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Vision 570 Modbus IP slave and master

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Hi everyone,

I am having real problems trying to get 2 v570's to talk via modbus ip at the same time as scada system reading from them both. I Currently have a PC scada system reading from the 2 v570's ok but also want one of the v570's to read from the other.

they both have 2 modbus configurations, the slave v570 has 2 scan-ex fb's one for the scada and one for the other v570 and the master v570 has one scan-ex and one read holding register fb,

i am using socket 2 for the scada system and socket 3 for the v570 using ports 502 and 503 respectivly with a socket init for socket 3, i have noticed that sb150 (socket 3 connected ) is 0

If i use some modbus scanning software i can access the slave on both ports so i'm sure the slave is ok but my read holding registers fb shows status of 5 and 0 acks.

I have attached only the modbus part of the software.

i think i must of done something stupid but i have now gone blind from looking at for so long so if anyone could cast an eye i would be very greatfull



v570modbusread slave.vlp


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  • MVP 2023

It looks like you have a number of problems that are easily resolved.

1) In the master, use a polling timer so that you are not trying to exchange data on every PLC cycle. I know MB 201 will prevent that, but a few extra milliseconds generally helps with MODBUS IP. I usually poll at 100ms intervals, but you can go much faster if you absolutely need to.

2) In the slave you do not need to configure socket 2 - you are scanning on socket 3.

3) Also, you are using SB 149 to gate your SCAN_EX FB - this will prevent the SCAN_EX FB from being executed. You should be using SB 146.

4) You do not need the SCAN_EX FB for the SCADA in your slave PLC.

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  • 1 year later...

Hello Everyone}

I  am a new for unitronics,

I need values advices  from  everyone.

I need to connect the existing V570 ( Master) with 4 new V570 (Slaves) 
My Goal is to show a status and values  of Equipments in 4 new V570  in the existing V570.

If possible to connect via above mention.

Please advice

Thank you


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  • MVP 2023

Yes, you have 4 sockets available for Ethernet communication. Initialize the 4 sockets and configure for MODBUS IP using the IP address and port numbers for the 4 slaves. Connect to each one and use MODBUS read commands to obtain the data you want. There are example projects that came with your VisiLogic installation that will demonstrate one way to accomplish all this.

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  • MVP 2023

@CallMeOme - you need to tell us how fast the data needs to update.  "As fast as possible" is not an answer - give us a real value you can live with.

I wouldn't use all 4 sockets in the V570 for Modbus IP - I generally leave a socket for myself for programming.

There are two ways I would do this-

1.  Use two sockets and alternate the IP addresses for the two slaves between them.  This will give you a possible update time of about 5 seconds.

2.  If you haven't bought the V570 for the Master (or can change your mind), I would seriously consider using a V700, which has 8 sockets.  This is a much better solution for what you are trying to do.

Joe T.

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  • 4 months later...

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