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Adrian

RS-485 connections and Modbus data access

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Hi,

I have a problem with commnunication, I try to connect a Nport5150 to Jazz PLC R31 wich has a MJ20-RS; but I have a problem with the connections, because the Nport has 3 pins ( Data A, Data B and "GND") and the MJ20-RS only has 2 (Data A, Data B , my question is, where can I connect the GND terminal?

And finally, i need help to acces the database of the Jazz PLC with MODBUS, i mean to the headers of MODBUS (eg. 0X:0, DW:10) I'm interesting only in the Jazz PLC R31.

PD. I have problems with my english, I'm starting to study, that's why I write as short as possible.

Thanks,

Regards.

Adrian G.

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Hi,

RS485 has two leads by default - Tx/Rx+ (A) and Tx/Rx- (B ). In case the port is not isolated, you need ot provide the same 0V refference to all the nodes in the network as condition for proper operation. I guess the GND there is in fact 0V of power supply (maybe internal DC power supply) of your instrument. You need ot connect it to 0V of 24V of the power supply of Jazz.

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There are many industrial products which have a reference to ABC for a modbus 485 connection. In my experience the c is actually only a polite place to give you to connect the shield drain of a shielded wire connection and not actually a 0V location. At least this is how it works when connecting to indistrial product with the same three available connections I have worked with in the past.

The second part of your question is relative to core modbus coding and what the data sructure is for the information you want to move from one place to the next and will be controlled by the version of Modbus that has been initialized in the devices you want to collect data from and to. You will be able to find manuals on standard modbus codign online, but I do not know what your native language is so I do not know if there will be something that will be easy for you to read.

Keith

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In fact the things are much simpler with Jazz and Modbus. As this protocol (Modbus RTU) is built in Jazz, you don't need ot learn its structure to be able to communicate.

As you describe the application, you need ot set Jazz as Modbus Slave and then to check Jazz Modbus Slave table topic to find the addresses you need ot set in your third party device/SCADA to read these addreses.

You can find relevant Help topics in U90Ladder > Help > Communication > Modbus (see attachment).

Good luck!

post-12-003198600 1313047941_thumb.jpg

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Hi,

Thanks for your answers.

I read the relevant help topics, and I tried with different settings combinations, for example, the time out, the baud rate. I found in the forum a program uploaded by Emil, which configure the Jazz PLC as Slave Modbus with RS232 Protocol, but I changed to RS-485.

I'am using SCADA/”Indusoft” and, NPort 5150 as a protocol converter from RS485 to TCP/IP. In the Scada the configuration of the driver is Modbus TCP.

I have a problem when the program tries to communicate with the PLC. The error is TIME OUT, but I have a method to know if the Nport and the Jazz PLC communicate. The Nport has a program with which, it monitoring the RS-485 port. The Nport reports 12Tx 1 Rx. This is the reason for what I asked previously for the RS485 connections.

Thanks,

Regards.

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What program have you started with to write the Jazz Modbus program? The standard U90 Ladder example is written for the M91 and won;t work on a jazz with the MJ20-RS4 (JZ-RS4) comms adaptor. You need an additional Com port ocnfiguration step.

Please see screen shot below for the critical step, added after the Modbus config rung. I have also attached the sample project files. I think these file was originally sent to me by Unitronics support, but IMHO they should be in the U90 Ladder examples.

post-16-061044200 1313107296_thumb.jpg

Modbus Slave Jazz RS485.U90

Modbus Master Jazz RS485.U90

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On 11/8/2011 at 7:03 PM, Simon said:

What program have you started with to write the Jazz Modbus program? The standard U90 Ladder example is written for the M91 and won;t work on a jazz with the MJ20-RS4 (JZ-RS4) comms adaptor. You need an additional Com port ocnfiguration step.

Please see screen shot below for the critical step, added after the Modbus config rung. I have also attached the sample project files. I think these file was originally sent to me by Unitronics support, but IMHO they should be in the U90 Ladder examples.

post-16-061044200 1313107296_thumb.jpg

Modbus Slave Jazz RS485.U90

Modbus Master Jazz RS485.U90

estoy utilizando esta configuración para comunicar JAZZ JZ20-J-R10 con modulo MJ20-RS pero no logro comunicarme con un OPC o SCADA, ¿cual es el numero del puerto COM del PLC ?

Modbus config module sets automatically port to 8,N,1. If other parameters needed, COM Init module MUST be after Modbus Config. no entiendo esta parte del texto

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Translated-

I am using this configuration to communicate JAZZ JZ20-J-R10 with MJ20-RS module but I can not communicate with an OPC or SCADA, what is the COM port number of the PLC?

Modbus config module sets automatically port to 8, N, 1. If other parameters needed, COM Init module MUST be after Modbus Config. I do not understand this part of the text

 

He's saying that the second rung in the program that configures the COM port must be set to your particular case.

What are the Modbus COM parameters for your SCADA system? RS-232 or RS-485?  The example is for RS-485.  Can you post your code?

Joe T.

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